.')2 Prof. T. R. Jones and ^fr. .1. W. Kiikbv on 



Thracia dissimilis. 



Ovate-ohlonc;, comprcssod, white, roughened by numerous 

 fine granules, which are generally arranged in lines radiating 

 from the umbo ; transversely excentrically j)laited ; 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 milHms., length 40, 

 thickness 15. 



This is nearly allied to T. plicata^vAxich Reeve (Conch. Icon. 

 Thracia, 7) considered it to be. Our shell is rather interme- 

 diate between T. jificafa and T. mognijicd, differing from the 

 former in ornamentation and general shape. On a tablet in 

 the British ]\Iuscum 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 fringed. The epi- 

 dermis along the posterior margin extends beyond the shell 

 and covers the bases of the siphons. 



EXPLANATION OF PLATE \1I. 



[All the fibres are of the natural size.] 



Fig. 1. Mactra anserina, right valve. Cumana, Venezuela. 



Fig. 2. Vent(s siiperba, right valve. Cumana, Venezuela. 



Fig. 3. Cardium ehurniferum, right valve. South coast, Trinidad. 



Fig. 4 a. Area centrota, right valve, interior. 



Fig. 4 b. The same, right valve of a large specimen, exterior. 



Port-of-Spain, Trinidad, Sept. 1874. 



VIII. — Xotes on the Palaeozoic Bivalved Entomostraca. 

 No. XI. Some Carboniferous Ostracoda from Russia. 

 By Prof. T. Rupert Jones, F.R.S., F.G.S., &c., and 

 James W. Kirkby, Esq. 



[Plate VL] 



In the seventh livraison of the first volume of his ' Lethaea 

 Rossica '* M. d'Eichwald figures and describes twenty species 

 of Palaeozoic P]ntomostraca, twelve of which are from the 



» We refer to the French edition, published at Stuttgart in 1860. 



