OF SOUTHERN INDIA. 413 



lb. Ilcmtellum, Bolten (1798), are called the narrow oblique forms, with 

 thin, often almost hyaline, radiately ribbed, inflated valves, with very distant beaks, 

 and a wide anterior gape; the type is Baclula hicms, Gm. fOstreaJ. 



Ic. Acesta, H. and A. Adams, 1855, was proposed for the recent B. excavata, 

 Chcm., an elongated, moderately compressed shell, with rather fine radiating ribs, 

 oblique in form, with the anterior ear very small, the posterior much larger, and 

 with the cartilage pit situated obliquely under beak, being excentric. Species 

 of this sub-genus already occur in the cretaceous period. 



Id. Flagiostoma, Sow., 1812, (Min. Conch., i, p. 175), must be reserved for 

 the species of the type of the liassic PL gigantea, for which it was originally 

 proposed. It is a very well marked group of fossil, especially mesozoic, Radulcc, 

 of a semi-ovate or sub-triangular shape, with nearly smooth or finely radiately 

 striated surface, the striae being generally only conspicuous at the sides of the 

 valves, but nearly obsolete in the middle; the ears are thick and unequal, the 

 anterior being smaller, and the cartilage pit is oblique and triangular, generally 

 very deep. 



\e. Limatula has been proposed, 1839, by Searles Wood for a characteristic 

 group of species of the type of B. suh-auriculata, Mont., the shells being narrow, 

 tumid, and almost equilateral, very Kttle oblique ; and the radiating strite or ribs 

 are only developed in the median portion of the valves. The type is well marked 

 already during the Jurassic, and the species are especially numerous during the 

 cretaceous period. 



1/. Ctenoides was used, 1753, by Klein for the almost equilateral, slightly 

 oblique, long, species of the type of Badula scabra, Born. The shells are hardly 

 gaping in front, the anterior margin almost straight, instead of being concave, 

 and the radiating ribs are numerous and scabrous. Species of this sub-genus also 

 occur in cretaceous rocks. 



Ig. Cteuostreoii, Eichw., 1SG7, (Leth. Ross., x-"" livr., p. 455). Sub-^qui- 

 valve, with strong radiating ribs, the large anterior margin above, or at the side, 

 with a distiuct byssal sinus; type, CL distcuis, Eichw., 1. cit., p. 456, from the 

 Neocomien of Russia. This is another well marked group of generally large and 

 strongly ribbed Bad nice, the shell of which is often irregular, like that of some 

 Sinnites ; when adult, it is characterised by the presence of a deep insinuation in 

 the anterior ear for the byssus, but in young shells this insinuation is hardly more 

 developed than in other allied forms. Lima proboscidea of Sowerby from jm-assic 

 deposits is another species of the sub-genus, and there are a few other mesozoic 

 forms which may be referred to it. 



2. Llmea, Bronn, 1831, (Italien's Tertisergeb., p. 115). Shell obliquely 

 roundly ovate, generally considerably inflated, radiately ribbed, slightly gaping in 

 front ; beaks prominent ; hinge-line slightly sloping and eared on both sides ; cardinal 

 margin internally with numerous teeth, divided in the middle by a triangular car- 

 tilage pit; muscular scar faint, sub-central; type, Ostrea strigillata, Brocc, 

 from tertiary deposits of Italy. Fossil species are known from the Trias in all 



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