ECHINOIDEA. 37 



in grooves which are narrow and deep near the apex, but quickly widen out and 

 flatten near the lower end. 



The interambulaoral areas are swollen, very narrow near the apex, where the 

 antero-lateral ones form a sort of short keel, which quickly expands ; the posterior 

 interambulacral area is very narrow, and was apparently raised into a low keel. 



The periproct is apparently elliptical, and situated on the truncated posterior 

 side, rather high above the border. Peristome unknown. 



The fasciole is well developed and peripetalous ; it is rather narrow and marked 

 with many rows of minute granules ; it is not very much curved, and round the 

 petals is slightly bent in apical direction on the interambulaoral areas. 



The ornamentation consists of small tubercles with low non-perforate mame- 

 ions which are surrounded by a scrobicula,r circle of minute granules ; on the upper 

 surface, above the fasjciole, the tubercles are rather sparsely distributed ; below the 

 fasciole they become more crowded and particularly on the anterior interambulaoral 

 areas, where they are also much larger ; on the lower surface they are again very 

 sparsely distributed, chiefly near the margin and on the plastron, leaving two smooth 

 bands ; the lower portions of the postero-lateral ambulacra are perfectly free. 



Locality and stratigraphical position, — Upper cretaceous series, horizon 4, 

 D^s valley. 



Bemarks. — Eemiaster indicus, Stol.j which has some similiarity with the species 

 described here, is easily distinguished by a shorter test, having a highly inflated 

 upper surface and a broadly truncated posterior side ; the profile line is therefore 

 quite different in both species. Semiaster siva is easily distinguished, not only 

 by its general shape, but chiefly by the different ornamentation and the conjugated 

 pores of the latero-ambulacral areas. 



HI. PELECYPODA. 

 I. Order : ANISOMYARIA. 

 1. Family : OSTREIB^, Lam. 



Gejius: OSTREA, Linne. 

 OsTREA ACUTiROS'jCEis, Nilsson. PI. IX., fig. 1-lb, 9-9a. 



( SjnoDymy io Coq.uand, Monographie du genre Ostrea, p. 75.) 



The shell, which attains a moderate size, is irregularly oval in shape, higher than 

 long, rather compressed and not strikingly inequivalve. The left valve is moderate- 

 ly inflated, slightly sloping in anterior, posterior and ventral directions. The umbo is 

 short but very pointed and slightly turned backwards. Ligamental pit rather short 

 and narrow. The surface is usually more or less f oliaceous, owing to strong striae of 

 growth, but sometimes, particularly in the central part of the valve, there appear 



