DISCUSSION

86

SMITHSONIAN MISCELLANEOUS

COLLECTIONS 94

NO. 13 STAPHYLINIDAE-

— BLACKWELDER

8/

entire classthatthere isan amazingvarietyof divergencein theless fundamental characters.

The

family Staphylinidae, being one of thelargest natural families of animals, is remarkably

homogeneous

ingeneral habitusand form,but presents considerablerangeof varia- tion in

many

ofitsstructures.

In agroupof this sizeit isto be expectedthat certain characters which are constant in oneseries of specieswill be

more

variablein others. Thisisfound frequentlytobe thecase.

A

certainsubfamily showsaregulardevelopmentofa given characterwhichthus charac- terizesit, but the

same

character

may

occur scattered here and there inother groups,being too variable for usein classification.

Beforeanycharactercanbe safelyusedin classification,itisneces- saryto

know

theextent of variation of that characterthroughoutthe group beingclassified. If it is reasonably constant and varies only indefinite

ways

andwithindefinite limits,thenitcanbe safely used.

If, on the other hand, it be found to be veryvariable within small groups, ortovarythrougha large

number

ofslightlyseparated forms,

itcanbeusedonlywithextreme care or onlyincertaincases.

The

range of variation in each structure or set of structures is discussed in detail in the section onthe comparative morphology of the family. It

may

be seen therein that the

amount

of variation in the

numerous

charactersdififersverygreatly.

Characters Available

forClassification

The

existingclassificationof theStaphylinidae,ashasbeenpointed out, is based almost entirely

upon

such characters ascan be seenin pinned specimens and with anabsolute

minimum

ofdissection,amount- ing to no

more

than the removal of a leg to permitits examination under a microscope.

The

study here

made

reveals a long series of structuresthat

may

beaddedtothelistof available characters.

Obviously, out of the

many

structures tobe seen onthe body of an insect, not all will be of aid in attempting a classification of the higher groups.

Some

are apparently usable only for theidentification of species;

some

appear only insmall groups such asgenera.

Some

areevidentlyvariable,andothers,consideredinthelightof thetotality ofstructures,

seem

tohave nophylogeneticsignificance.

We

are

com-

pelled,then,to exercise a certaindegree of judgment, based

upon

an examination of as

many

species as possible, in selecting those char- acters which will probablybe significant as afifording bases for de- finingthevarious categories.

Out

of the surveyhere presented the followinglist of characters hasbeenselectedasofi^eringprobablythe

6

88 SMITHSONIAN MISCELLANEOUS

COLLECTIONS VOL. 94 most significant indications of relationship. That is, they present tangible differences between the various groups, while at the

same

time they are of sufficient constancy throughout any one or

more

groupstopresentan appearanceof reliability. Itisevident,however, thatonlyan examinationof averylarge proportion of the species of thefamilycan permit adependableevaluation.

The

following are the structuralcharacterssuggested

1. Condition ofthecoronal suture.

2. Condition of theepicranialarm orfrontal sutures.

3. Conditionoftheclypeal area.

4. Condition of theoccipital suture.

5. Position oftheantennalfossae.

6. Presenceofocelli.

7. Absenceofdorsaltentorialpits.

8. Conditionofthe gular area.

9. Segmentation of theantennae.

ID. Presence of processesonthelabruni.

11. Dentition of the mandibles.

12. Conditionofthe prostheca.

13. Presence ofserialporesonthemandibles.

14. Relativesizeandshapeofthe laciniaandgaleaofmaxillae.

15. Segmentationof themaxillary palpi.

16. Size and shape of the terminal segments ofthe maxillary palpi.

17. Shapeofthesubmentum.

18. Shapeofthe glossaeandparaglossae.

19. Segmentation of the labial palpi.

20. Shapeoftheterminalsegment ofthelabial palpi.

21. Condition of postcoxal lobe of pronotum.

22. Condition ofthe prosternalarea.

23. Enclosureofthe front coxal cavities by various means.

24. Condition of mesothoracic peritremes.

25. Presenceofcorneous platesintheanteriorforamenofprothorax.

26. Separationofmiddle coxalcavities.

27. Condition of elytral suture.

28. Segmentation ofthetarsi.

29. Specially modified setae of the legs.

30. Trochantero-femoraljoint.

31. Structureandposition ofthe posterior coxae.

32. Conditionofsecond abdominalsegment. !

33. Paratergites ofabdomen.

34. Mosaicpatterns ofintersegmental membranes ofabdomen.

35. Presenceof gonapophyses inmale genitalia.

36. Conditionof lateral plates infemale genitalia.

27. Modificationsof the aedeagusin the male.

38. Condition of valvifers, coxites, paraprocts, and proctiger in the female genitalia.

39. Modificationsof theeighth segment in thefemale.

40. Condition ofthe ninthand tenth segments in the female.

no. 13

staph

ylinidae

— blackwelder 89 The Value

of

Existing

Classifications

and Some

Suggestions

Concerning Them

As

far as the present study is concerned, no major changes are indicated inthe existingclassificationof the higher categories of the family.

However,

there will be

numerous

changes in position or in therelativedegreeofisolationof certaingroups.

It hasbeen very frequentlynoted that the conventional statement ofa character used in a classification

may

have no precise

morpho-

logical

meaning

except as indicatingthat

some

peculiarityexists.

Some

of these characters are discussed below.

The

presentsubfamilyclassification,as wellasthat ofallthesmaller categories, is toa largeextent based on^"key^" characters. Thatis,

there has generally beenin this family nodistinction between classi- ficationandidentification. This haslednecessarily toa system based onobviousand readilyobservable characters, rather thanon theones particularly suited to

show

the fundamental relationships.

Each

of these characters hasbeendiscussedbyitselfinthecomparativesection.

The

diflferences between existing classifications are chiefly those of the differences of opinion regarding the isolation of each group, and the components of ^it, and are to a large extent due to the use of an insufficient

number

of categories. Although the family un- doubtedly contains several large and

homogeneous

groups, there are alsoa

number

ofveryisolatedand extreme forms which have no very close relatives and are yet obviously

members

of the family.

Some

authors tendtounitethesewiththeirnearestneighbors,whereasothers attemptto

show

the great divergenceby separating

them

as distinct tribes or subfamilies.

The

purpose of classification is to

show

not only the relationships between animals but also the degree of the differencebetween them.

In

European

catalogues thegenus Micropcplushassometimes been united with the subfamily Omaliinae.

More

frequently, however, ifis given subfamily rank. Itseldom showsthe typicalstructure of the family buthas several modifications notfound elsewhere. Itap- pearstobe

more

isolated

from

alltheother Staphylinidsthantheex- tremes of that family are

from

each other. It istherefore thought probable that it will haveto be

removed

asa separate family. This has alreadybeendoneby

some

writers.

In the

Leng

Catalogue (1920) Proteimis, Leptochirus, Eumalus, Trigoniiriis,Phloeocharis,and Pseudopsisareunitedinthesubfamily Piestinae, and thereby are separated

from

the Oxytelinae. In the catalogue ofEichelbaum (1909) these areallincludedinthe Oxyteli-

go

94 nae.

They

havesufficientcharactersin

common

whichdiffer

from

the Oxytelinitojustifya separationbetweenthetwo groups. Leng'sar- rangementisperhapsbetter forthisreason.

Osoriiisis quitedistinct in

many

respects

from

the Oxytehni. Its relationshipisperhapsbest expressedby an assignment asatribe in thesubfamily Oxytelinae equal to the rest of the subfamily or the tribeOxytelini.

The members

of the Xantholinini studied are very distinct from therestof the Staphylininae.

They

differ

from

thetribe Staphylinini

more

thando^the

members

of thetribes Xanthopygini andQuediini, and perhaps should be

more

isolated in the system. ^It

may

bethat theyshould rankasaseparate subfamily, butthis wouldobscure the factsoftheirrelationshiptotheother Staphylininae.

Habrocerusand

Hypocyptus

bothdifferconsiderably

from

the other Tachyporinae. Habrocerusdiffersperhaps

more

widelyand is prob- ably correctly placed as a separate subfamily, although its nearest relativesare the Tachyporini.

Hypocyptus

is

more

distinct

from

the Tachyporini and Bolitobiini thanthey are

from

eachother, but per- haps insufficiently soto be isolated ina separate subfamily.

The

linear arrangement of subfamiliesis unsatisfactory as it pre- cludes thepossibility ofshowing relationshipsexceptin special cases.

No

better system has been suggested, and it ismerely necessary to bear in

mind

the factthatthe arrangementis

more

orless arbitrary.

The

classifications in use have been gradually improved to the point where they seemto reflectthe general facts in a true picture.

Minor

refinementswillprobablybe necessary for a longtimetocome, andthejudgment of individualworkers will probably indicate

many

changes.