Little can be said about the details of either the existing climate or vegetation of a large part of Bolivia. Fossil plants abound in the latter on the north-eastern slope of the mountain and also in some of the mine tunnels. Similarly, all the non-leguminous genera except Myrica and Weinmannia are represented by a single species.
The balance of the species occurs throughout the Antilles, Central America and northwestern South America. Eastern North America is therefore ... the only region where there is any significant overlap of the two subgenera. It is therefore clear that the known method of determining the age of the Potosi flora by direct comparison with fossil floras of.
I don't think the similarity to recent flora east of the Andes is overstated, but the remarkable discovery of a marine Brachiopod in the Potosi tuffs added another factor. At present, the eastern slopes of the Cordillera Real are climatically and therefore very different.
PTERIDOPHYTA
No brachiopod has ever adapted its seK to freshwater, although Lingulas continue to live in the very fresh water of the present marine margin. When it comes to making comparisons with extant species of Polystichum, difficulties are almost insurmountable for several reasons—namely, the insufficient amount of fossil material, the variability of the recent species, the lack of sufficient comparative material, and the difficulty of connecting mere names or frequent species with actual specimens. He has been good enough to examine the fossil for me, and regards it as allied to the historical and extreme.
These, while showing the generic fikeness of a fossil, are not particularly close to it. Lomariopsis is a characteristic genus of tropical forests of both hemispheres with relatively few but highly polymorphic extant species. There are some small fragments in the present collection which appear to have the venation Acrosti-.
Description.—This somewhat doubtfully identified form was described from Potosi by Engelhardt and has not been recognized in more recent collections. Gymnogramme has numerous species existing in South America, to which region it is practically limited and is well represented in the drier regions of the high Andes from Colombia.
CONIFEROPHYTA
Without looking at the original material, it is impossible to draw conclusions about its validity. This characteristic type is represented in fragments in the present collection, but the entire sheet is reproduced from Engelhardt's figure. It clearly refers to Podocarpus belonging to the section Ewpodocaryus of Endhcher, and is comparable to the extant Podocarpus lamberti Klotzsch of central and southern Brazil.
The extant species of Podocarpus are over 40 species, and they are as dominant representatives of the Coniferales in the southern hemisphere as the pines in the northern. Jamaica and Central America in the Western Hemisphere, and has representatives in all three of the large southern landmasses, as well as in Madagascar and New Zealand. This distribution suggests a long geological history, in accordance with which certain forms from the British Jurassic and Lower Cretaceous and the American Lower Cretaceous are referred to the genus Nageiopsis. be elevated to its former position of generic rank.
All of these are very similar and the fossil can be successfully compared to almost any of them. Podocarpus is not at present found west of the Andes, but is represented by two or more species in the forests of the eastern slopes, the so-called Ceja region of Herzog.^ In northern Peru it is also found in the lateral valleys within the frontal region, the most widespread form is Podocarpus oleifolius, a shrub or arborescent form, which at 6° latitude reaches heights.
ANGIOSPERMOPHYTA
It is clearly distinguished from the other members of the Potosi flora and apparently represents a striking Comptonia-like Myrica. Midrib thin but prominent on the underside of the leaf, tending to be flexible. Of the latter, the pctiolule form depicted in this context may be of a different species, but is otherwise indistinguishable.
The genus Copai^era includes about 16 extant species from the equatorial region of Africa and America, ranging from the West. It is not represented in current collections, but was compared by Engelhardt to the extant Dalbergia riparia Bentham from the Amazon basin. This species is well marked and easily distinguished from the other members of the Potosi flora.
It is clearly distinguished from the other members of the Potosiflora and was compared with the extant Sweetiaelegans Bentham, a Brazihan species. This species was described from Potosi by Engelhardt, who compared it with the existing Lonchocaij MSobtusus Bentham of the Bra-.
LEGUMINOSAE INCERTAE SEDIS
The fossil species closely resemble the extant Porlieria Jiygrometi^ica Ruiz and Pavon of the arid country between southern Peru and northern Chile and Porlieria lorentzii. It is one of the few fossil species found at Potosi that clearly indicates arid conditions, and this may be because it grew on a porous slope where solar radiation was high – i.e. Description.—This record was based on an obscure specimen preserved in a coarser-grained rock than the rest of the Potosi flora, and considered by Britton to possibly represent a nodulose stem of some fleshy Euphorhia which still characterizes the extant flora parts of South America.
The basal half of the leaf forms an almost exact semicircle, and the crenulations of the margin become obsolete in the basal region. 155 Primaries three, stout, diverging from the outermost base at angles of about 40°, the central almost straight and the laterals slightly curved outwards, each terminating at the apex of the obtuse lobes. Tertiaries obsolete by immersion, from the character of the margin, probably camptodrome as in the newer species.
This species is not represented in the current collection and the accompanying illustrations are taken from Britton's report. The latter author doubts the reference of these leaves to Passifiora, but I see nothing to criticize in this provision. The marginal character and peculiar aspect of the leaves, with their broadly rounded base, obtuse lobes and elongated elongated central lobe, and with the basal primary leaves, clearly indicate them as referring to the Passifloriaceae, a family abundantly represented in the existing floraofvSouthAlnerica.
I don't know if Passiflora currently occurs in Bolivia, west of the Andean front region, but it is not uncommon in eastern Bolivia, and according to Herzog a species occurs in the Andean foothills of Santa Cruz and Cochabamba, higher on. up to an altitude of 2,600 meters. According to Britton, the current strain is closely comparable to the fruits of the extant TerminaliaoUongaPersoon collected in Guatemala. It is an ancient type and the modern species are divided into four sections based mainly on the characteristics of the fruit, which can be fleshy, woody or differently winged.
The majority of these, especially those in the Mississippi depositional region, appear to have been littoral species such as the modern Terminalia catappa and Terminalialittoralis. Usually there is a basilar or subbasilar plane primary on each side that diverges from the midrib at different angles and merges with the secondary venation at or above the middle of the leaf. With the exception of Ouphea halsamona in the Galapagos and Sandwich Islands, it is restricted to America and there mainly in the equatorial and subtropical regions.
GAMOPETALAE
This species is known only from material in the Potosi collection studied by Britton and may therefore be less common. Cuphea is a large modern genus with about 160 extant species of herbs and shrubs, otherwise unknown in the fossil state. Gaylussacia has many extant shrub and subshrub species that are widely distributed in the Western Hemisphere from the equator to the northern and southern temperate zones.
Secondaries distant, diverging from midrib at wide angles, straight to near margin, where their ends are joined by flat arches. Thin percurrent veins subparallel to the arches are usually halfway between them and the midrib. The shape and especially the venation warrant the referral of this form to the Apocynaceae, which have a large number of shrubs, trees and leaves in tropical South America.
Secondaries thin, numerous, ascending; they depart from the center at acute angles, which are subparallel to each other and the lateral margins, and are connected by straight oblique tertiaries. We hesitate to place this well-marked new form in the genus Jacaranda, which matches the leaflets of several extant pinnate-leaved species with small leaves, such as Jacaranda caroliniana Pohl or JacarandacuspidifoliaMartius. The genus Jacaranda comprises about two dozen extant species of shrubs and trees.
There are poorly preserved specimens of several varieties of winged seeds in the Potosi collections, but none of these can be conclusively referred to the Bignoniaceae. According to Herzog' Jacaranda cuspidifolia occurs in the vicinity of Santiago and San Jose and in the hill country of Velasco and a second species is found in the broken forests along Rio Pirai and Rio Yapacani, all places in eastern Bolivia. Description.^Le&res small, ovate, or broadly elliptic in outline, relatively long petiole, broadest in the middle, with a somewhat narrowed rounded tip and a broad spiky base.
These small leaves are somewhat suggestive of some species of Celastraceae, but in general their closest affinities seem to be with several extant genera of Rubiaceae, and thus refer to the form of the genus Ruhiacite proposed by Weber for Rubiaceous leaves of unclear generic affinities. Coprosma comprises about 40 species of shrubs and small trees, mostly eastern and ranging from Java to New. Palicourea comprises more than 100 species of shrubs that are restricted to tropical America and range from Mexico and the Antilles to southern Brazil.
INCERTAE SEDIS
There is such a variety of unrelated plants in the modern flora of the tropics, including ferns, various monocotyledons and numerous dicotyledons, which slender stems with stalks in the small frag-. As an additional element in the Potosi flora, this specimen deserves to be placed on record.
EXPLANATION OF PLATES
