52 Prof. T. R. Jones and Mr. J. W. Kirkby on 
Thracia dissimilis. 
Ovate-oblong, compressed, white, roughened by numerous 
fine granules, which are generally arranged in lines radiating 
from the umbo; transversely excentrically plaited ; anteriorly 
rounded; posteriorly vertically truncate, with a keel (most 
prominent on the smaller valve) running from the umbo to 
the lower posterior angle. Height 27 millims., length 40, 
thickness 15. } 
This is nearly allied to 7. plicata, which Reeve (Conch. Icon. 
Thracia, 7) considered it to be. Our shell is rather interme- 
diate between 7. plicata and T. magnifica, differing from the 
former in ornamentation and general shape. On a tablet in 
the British Museum the name dissimilis is applied to our 
species; but I have not been able to find any authority for 
that name, which I adopt for the shell. 
The animal is furnished with two long siphons, separate for 
the whole of their length and coarsely frmged. The epi- 
dermis along the posterior margin extends beyond the shell 
and covers the bases of the siphons. 
EXPLANATION OF PLATE VII. 
[ All the figures are of the natural size. } 
Fig. 1. Mactra anserina, right valye. Cumana, Venezuela. 
Fig. 2. Venus superba, right valve. Cumana, Venezuela. 
Fig. 3. Cardium eburniferum, right valve. South coast, Trinidad. 
Fig. 4a. Arca centrota, right valve, interior. 
Fig. 4b. The same, right valve of a large specimen, exterior. 
Port-of-Spain, Trinidad, Sept. 1874. 
VIII.—Notes on the Paleozoic Bivalved Entomostraca. 
No. XI. Some Carboniferous Ostracoda from Russia. 
By Prof. T, Rupert Jones, F.R.S., F.G.S., &e., and 
James W, Kirxpsy, Esq. 
[Plate VI.] 
In the seventh liyraison of the first volume of his ‘ Lethea 
Rossica ’* M. d’Eichwald figures and describes twenty species 
of Paleozoic Entomostraca, twelve of which are from the 
* We refer to the French edition, published at Stuttgart in 1860. 
