THE OSLRACODOUS GENUS BAIRDIA. 565 
44, Duscriprion of the Sprcrus of the Ostracopous Grnus Barrp1a, 
M‘Coy, from the CARBONIFEROUS StRATA of GREAT Brirain. By 
Professor T. Rupert Jonrs, F.R.S., F.G.8., and Jamus W. 
Krrxsy, Esq. (Read May 28, 1879.) 
[Puates* XXVIII.-XXXIT. | 
Tru genus Bairdia was instituted by Professor M‘Coy, in 1844, for 
the reception of two species of Entomostraca from the Carboniferous 
Limestone of Ireland. Since then other species belonging to the 
same genus have been described from the rocks of the same age 
occurring in Scotland, Bohemia, Russia, and Australia; and many 
species have been made known from the Silurian, Permian, Triassic, 
Jurassic, Cretaceous, and Tertiary strata, as well as from existing 
British and foreign seas. 
The recent forms of BSairdia are all marine, and are found at 
various depths, ranging from 10 to 500 fathoms; and the Carboni- 
ferous species (and those found in other formations) occur in lime- 
stones, and calcareous ironstones and shales, together with Corals, 
Crinoids, Polyzoa, and marine Shells of all classes. 
Bairdia, in fact, is exceptionally marine in its mode of occurrence 
in Carboniferous strata. Other marine genera of Paleozoic Ento- 
mostraca often have some stray species occurring with equivocal 
associates. Leperditia, for example, which is a markedly marine 
genus, has one representative, L. scotoburdigalensis, met with as a 
very common fossil in the Calciferous-Sandstone series of the east 
of Scotland, where it repeatedly occurs with the remains of Lepi- 
dodendron, Sphenopteris, and Ganoid Fishes. Beyrichia, another 
marine group, has B. arcuata as a Coal-measure species, occurring 
with Plants, Fishes, and other fossils characteristic of that forma- 
tion, but of dubious habitat. And so with Airkbya, all the species 
of which are marine, though at times two of them, K. plicata and 
K. spiralis, appear in Lower-Carboniferous strata with Sphenopteris 
afims, Lepidodendron, and Stigmaria. 
We do not say that such doubtful companions indicate purely fresh- 
water habits on the part of these Entomostraca, though such occur- 
rences must mean differences in physical conditions compared with 
those prevailing during the formation of the limestones and other 
calcareous beds in which the species of these genera are usually found. 
Among the Bairdiw we know of no such exceptions to the rule; 
they never occur with Fish- or Plant-remains. In the thin lime- 
stones intercalated in the thick Calciferous-Sandstone series of Fife- 
shire B. plebeia, B. Hisingeri, and Leperditia scotoburdigalensis occur, 
with Orthoceras, Murchisonia, Schizodus, and other marine shells; 
but the Bairdie always disappear, as well as the Mollusca, in the 
* The cost of lithographing these Plates has been defrayed by a grant from 
the Royal Society. 
