OE SOUTHERN INDIA. 25 



The surface of our species is very minutely striated, and the upper posterior 

 margin lamellar. The narrow post-umbonal plate lying between the margins of 

 the yalyes is stilet-shaped, posteriorly ending in a point; the ventral one is of 

 similar form, but longitudinally divided by a groove. The front edges of the valves 

 below the umbones are slightly elevated, and the region next to them impressed. 

 The species can be easily distinguished by its regular club-shaped form and fine 

 striation on the central area from Mart, (Farapholas ?J sanctce-crucis, Pictet; a 

 more closely allied species to ours is the recent Martesia calva, Sow. 



Locality, — Moraviatoor ; boring in wood. 



Formation, — Ootatoor group. 



II. Family— OASTBOCHjENIDu^. 



The animals, belonging to this family, in many respects resemble those of the 

 FsoLABiD^ ; they are generally symmetrical, claviform, with a short sub-cylindrical 

 foot which is not byssiferous, although occasionally provided with a byssal groove ; 

 the mantle margins are thickened, often prolonged into various cirrhi, or other 

 appendages, united along the ventral side ; there are two gills on either side, but their 

 size varies, the outer ones are often larger than the inner; they are more or 

 less prolonged into the siphons, which generally are united up to near their ends. 

 The shell consists of two equal, or very nearly equal valves, which are thin and 

 inequilateral, more or less gaping in front ; the hinge teeth are rudimentary or alto- 

 gether wanting, the beaks being, however, occasionally supported by a small internal 

 lamina; the ligament is external, but usually very small and thin; a portion of it 

 sometimes reaches to the internal edge, representing the cartilage. The valves are 

 either free, enclosed in a shelly tube, or more or less grown together with it. 

 Deshayes in his last edition of the Paris fossils again dwells in great detail upon the 

 idea (which he formerly advocated) of the temporary separation of the valves from 

 the tube during certain stages of growth. The course of growth appears to me not 

 to offer anything peculiar or extraordinary. It is nothing but an organic — may be 

 acid — secretion which constantly dissolves the edges of the aperture in the Gastro- 

 poda when they grow largely, and exactly the same takes place at the edges of the 

 valves of Felecypoda, 



There are three somewhat different groups of shells which belong to this 

 family. Tryon published a monograph of the family in the Proceedings of the 

 Philadelphia Academy of Natural Science in 1861, and a revised list of the 

 species in 1867, part 3, vol. iii, of the American Journal of Oonchology. This 

 last publication is the most complete one available, and in giving here a short 

 review of the various types, I shall follow it with a few slight alterations. 



G 



