Stimpsoi' undertook their classification and arrangement in the Museum of the Institution. The real difference between this group and the Littorinidta is in the shape and position of the teeth on the lingual strip. 34; because Leach had already applied it to a genus of insects.” But the name of the Coleopteran genus is Hydrobius.
AND ALLIED FORMS
Gould, except brief accounts of the gills and of the nature of the ova, which do not agree with my own observations, as detailed below. 590, gives a more detailed account of the animal, and points out certain similarities with Melania and TruncateUa. The author states that his knowledge of the anatomical features is mainly due to Moquin-Tandon, and it will be noted that this is an exact translation of Moquin-Tandon's description of the anatomical features.
10 RESEARCHES UPON THE HYDROBIIN^
AND ALLIED FORMS. 11 often seen the auricles of tliG foot in Amnicola jjorafa, in certain
12 RESEARCHES UPOX THE HYDROBIIN^
ON THE AMEPJCA?^ FRESH-WATER HYDROBHNi
AND ALLIED FORMS. 13 vibrated laterally until their tips met in front, and tlicy inclosed
14 RESEARCHES UPON THE HYDROBIIN^
AND ALLTKD FORMS, 15 two outer ones large. The upper margin of the rhachidiun tooth
16 RESEARCHES UPON THE HYDROBIIX.E
Moquin-Tandon, in his work on the terrestrial and liquid molluscs of France, published in 1856, regarded all the fresh-water rhissoids of that country as belonging to a single genus, B^thinia, which he divided into two subgenera : Fiona, synonymous with the true Bytliinia of Gray, and Bythinella, JVIoq.-Tand., comprehending numerous small snails belonging to our subfamily Hydrobiin^. The group Bythinella, as suggested by Moquin-Tandon, contains at least two distinct genera, neither of which is synonymous with ourAmnicola; but the name must be reserved for the forms related to B. I have not been able to obtain specimens of this European true Bythinella3 for examination as to their lingual dentition; but Troschel, in his work already frequently quoted, figures the teeth of a species called by him "Amnicola (Suhulina) thermalis,^'" — which is probably related to the true Bythinelloe, the Turbo thermalis of Linnteus which is anew.
18 RESEARCHES UPON THE HYDROBIIN^
19Under: the synonyms of Fraueiifeld we find the name of Microno. Below: the synonyms of Fraueiifeld we find the name of Microno. Indeed, I have not had the opportunity of examining the entire soft parts of any of these species, nor of determining the shape of their eggs—except in one single case, on which I could rely. Given the shape and blunt top of the shell, and the character of the teeth, I have no hesitation in recommending the Palu-.
20 RESEARCHES UPON THE HYDROBIIN^
22 RESEARCHES TPON THE HYDROBIIN.!;
AND ALLIED FORMS. 23 chidian tooth, which is quite different in form from that of S
Leahas described and figured a shell (Fig. 15, enlarged) from the Columbia River, Oregon, under the name PaludinaNuttalliana. It is also so similar to that of the allies of Paludinadecisaand, that it is not at all surprising that their proximity should have been referred to by the eminent naturalist who first described it, as the unknown operculum. In fact, we find it to have the same shape, the same eroded apex and olive periostraca, and the same form of aperture with prominent outer rim and sinuate base, which are characteristic of Eastern Melanthos (Campelomse).
These characters of the shell and its opening will serve to distinguish the new genus Fluminicola, which the species considers for its type, from other Hydrobiinae. The shell (Fig. 15) may be described as follows:—It is rather .. thick and strong, subglobular or subovate to conical, imperforate and simply striated. Diaphragm ovoid, anteriorly rounded, angular; columella concave, flattened and numb, especially near the umbilical region; margin of the peritreme not in the same plane, but sinuate.
The eyes are barely perceptible, and are located on slight protrusions at the outer bases of the tentacles. The gill (Fig. 16,dl) is very broad in front, but becomes narrower behind; it consists of about twenty layers of subtriangular plates, many. The rim (Fig. 16, h) is large, flattened, broader than long, and placed obliquely on the right side of the neck, a little distance behind the right tentacle.
The oviduct of the female lies on the sheath parallel to the rectum and fills the space between this latter sac and the line n.
26 RESEARCHES UPON THE HYDROBIIN.E
Theodore Gill, in recognition of his great ability as a malaeologist, and of the assistance he has rendered me in determining the conchological characters of the animals now under consideration. The shell in this genus is thin or only moderately thickened, simply striated, short, subacute, barely umbilicate and with a body whorl subspherical, the tip is rather small and the suture is not impressed. The aperture is ovoid, regularly rounded in front, angular behind, with the peritreme thin and sharp, compressed inwards behind into a curl, and with the whole edge in the same plane, which is very oblique, inclined downwards and upwards.
The soft parts of Gilla altilia are similar to those of the previous two genera in the robust shape of the body and snout, but they differ. The eyes are located on the outer sides of the tubercles at the outer bases of the antennae. The colors of the animals are more reminiscent of the Melanians than those of Amnicola, being very dark and finely mottled, as if peppered.
28 RESEARCHES UPON THE HTDROBIIN^
AND ALLIED FORMS. 29
ON THE SUBFAMILY POMATIOPSINil
30 RESEARCHES UPON THE HYDROBIIN^
Without further preface I will proceed to describe the soft parts of the species of the genus. It is much broader than the Amnicola, and may project forward somewhat in front of the rostrum, notwithstanding the considerable length of the latter. The lateral surface of the body and foot represents a system of sinuses adapted to the special way of advancing the animal, which will be described below.
Above this there are two oblique folds arising from the lower base of the nest and extending upwards and backwards, the upper reaching to the base of the tentacle, and the lower extending up along the side of that constriction of the body which is. They are not able to rise in the air, but hang down, hanging from the side of the head and resting against the base of the stand. The eye is located on the outer side of a rather pronounced swelling of the outer exit of the head at the base of the tentacle.
It is of large size, and if expanded would reach the middle of the rostrum. But the apices of the two lateral teeth differ considerably from those of that species, as each is 5-toothed, with the teeth unequal. It will be noted that, among the several prominent features of distinction between this dentition and that of the Hydrobiina?, that the basal denticles of the rhachidial tooth in Pomatiopsis are placed at or near the base.
To conclude this description, I will give an account of the manner in which the step mode^ progression of Pomatiopsis.
34 RESEARCHES UPON THE HYDROBIIX.^
In crawling, the movement is similar to that of loop or geometric tracks, with suction cups attached alternately. Before concluding our remarks on this sub-family, the very great resemblance to Fomatioj^^sis must not be forgotten. shown in the genus Tomicliia of Benson, which most writers place among the air-breathing snails of the order Operculata, sul)order Opisophthalma, and family TruncatellidiE. 34;Adult specimens were mostly crawling on moist soil at the edge of water; but the younger individuals were submerged."^ Such habits seem to indicate, at least in the young, a branchial rather than pulmonary mode of respiration.
The better position of the eyes may be of little importance; butitis found, in other cases to coexist with respiratory organs that are formed for breathing. The lingual dentition, as figured by Troschel,^ is in all respects similar to that of Foniaiiopsis, except that the rhachidial tooth has its basal denticles connected by a transverse plate ; - a character that approximates it with the Truncatellidae. Three genera have recently been described in the "Annals and Magazine of Natural History," which have considerable resemblance in former habits, or in both, to the Pomatiopsinae.
Unfortunately, the linguistic dentition of these genera, which would provide the best guide to their true position in the system, has not yet been studied. 34;lunger,"^two of which must be referred, with Ibmichia, etc., to the neighborhood of Truncatellidfe, while the other will form a new family. Blanfordia shows an even greater resemblance to Pomatiopsis than does Cecina, for we find in it the same arrangement of lobes and sinuses in the sides of the foot, indicating the same step-form of progression; but this is accompanied by the truncateloid character of having the eyes on the upper bases of the tentacles; so that the genus will probably be found to belong to the Truncatellidce, when its respiratory organs and dentition be investigated.
It has a trochiform shell that is very different from that of Cecina and Blanfordia and approaches that of the marine genus Fossarus.
38 RESEARCHES LTON THE HYDROBIIN^
AND ALLIED FORMS. 39 from Bythinella and Paludestrina, and the same difficulty will
40 EESEARCHES UPON THE HYDROBIIN^
Benson says that the soft parts resemble those of Melania, but the characters he gives of these parts do not serve to distinguish them from those of the Hydro-. This species is the Cyclostoma acutum of Drapaniaud, a brackish water or marine species, identical to the Turbo ventrosus of Montagu. The characteristics of the soft parts of this species, including its lingual dentition, are as yet unknown, but its shell is so similar to that of the common "Cingula minuta" from the New Eng coast.
AND ALLIED FORMS. 43 that species is decided with some degree of certainty, materials
Adams^ has correctly understood Pfeiifer's genus, as their description shows, but most of the species they mention, including our Littorinella minuta, belong to entirely different groups. This genus differs from Amnicola in its lingual dentition, the rhachidian tooth having only one basal tooth. Lesueur's name is regarded as synonymous with Loligopsis by Gray,^but the group appears to be sufficiently separated from the typical Loligopsids in the tuberculation of the body.
As in all such cases, we must choose a type from those described by him, and of these we select the first, not only because of the conformity of such selection to a generally accepted rule of nomenclature, but because it will furnish us with a name for a group of American forms that are generally separated from the other elongated freshwater species we included in Bythinella. The first species ever described by D'Orbigny, as far as we have been able to determine, is the P. This species is called by the author "commonly occurring on the maritime sands of Cuba", which immediately suggests the idea that it may be a Hydrohia or Rissoa, and unrelated to the South American freshwater forms we have included in the genus, from one of which the lingual dentition of the genus is derived.
AND ALLIED FORMS. 4T shells of Cuba/ and D'Orbigny himself says that the species was
48 RESEARCHES UPON THE HYDROBIINM!
AND ALLIED FORMS. 49 projection of the outer lip, which gives it a character somewhat
50 RESEARCHES L'PON THE HYDR0BIIX.5
Lingual dentition of the type: Rhachidian tooth moderately long, deeply trilobate below; basal denticles near the basal margin and extending further. Shell rather large, globose, thin, smooth, perforated; pointed small; suture impressed; body globose, more or less shouldered above.
52 RESEARCHES UPON THE HYDROBIIN.E
THOGI.YFHUS, Muhlfeldt
Shell spherical, thick, smooth, imperforate; spire short; bond not pressed. Opening broad swollen, or almost circular, almost as wide as long; inner lip calloused; outer lip simple.
54 RESEARCHES UPON THE IIYDROBIIN^
AND ALLIED FORMS. 55
ADDENDA ET CORRIGENDA
INDEX
58 INDEX
