OF SOUTHERN INDIA. 107 



The ScROBicvLARiiB^ are principally cliaracterized by the great length and 

 thinness of the siphons and a comparatively thin shell with an internal straight or 

 oljlique and posteriorly directed cartilage-pit. There is a remarkable similarity in 

 all the shells which entitles their forming a special group, distinct from the Tellens. 

 This separation is also justified by geological research. There are as yet no 

 thoroughly reliable proofs of any species of this family occurring in mesozoic rocks, 

 though some cretaceous species seem to be strongly indicated ; those from tertiary 

 deposits are not very numerous.* Of recent species there are about 120 species! 

 known, and of these certainly one-half belongs to the genus Semele. The Indian 

 seas contain representatives of most of the genera and a large number of species. 

 Those of the Cumingia group are perhaps most imperfectly known, and many 

 additions may, I believe, be expected from Indian seas. 



a. Sab-famili/,— CUMIN GIINM 



Most of the species of this sub-family burrow in corals and stones, like 

 PetricoliB, and the concentric striae are therefore very sharp and prominent ; the 

 foot of the animals is generally very small. 



1. Cumingia, Sow., 1833. Shell transversally elongated, gaping posteriorly ; 

 hinge -vvith a projecting oblique cartilage process, in front of Avhich there are usually 

 two thin laminar cardinal teeth in the right, and one — occasionally bifid — in the left 

 valve ; one distinct lateral tooth on either side, both stronger in the right than in 

 the left valve. The species of Cmningia are usually found burroAnng in corals. 



H. and A. Adams state that there are no lateral teeth in one valve. I have 

 examined five species of Cmningia from the eastern seas, and all certainly had the 

 laterals in the right valve stronger, but by no means obsolete in the left one. 

 Deshayes describes the animal and shell of a Cum. gvandis, which is remarkably 

 elongated, posteriorly attenuated, very much like a Si/iidosm>/a, and also apparently 

 of a much thinner structure ; it could probably form a distinct section of the genus, 

 for its habitat seems also to be different from that of other CumiugicB (see Jour. 

 de Conch., vol. v, 1856, p. 378, &c.). 



2. Montrouziera, Souv., 1863, (Journal de Conch., 3"^ ser., vol. ii, p. 282). 

 Shell moderately elongated, hinge Avith the cartilage in a posteriorly directed 

 groove, two cardinal teeth in front of it in the right valve, a single triangular, bifid 

 one in the left ; posterior but quite close to the cartilage-pit there is in each valve one 

 short lateral tooth, looking, however, more like a posterior cardinal. Souverbie's 

 type species M. clathvata is from New Caledonia. I have also examined a 

 new species which Mr. G. Nevill collected at Mauritius; it is similar in form to 

 the last, having the posterior lateral (cardinal ?) teeth very small, thin, and in the 

 left valve almost obsolete ; thus it very closely approaches in character to the next 

 genus, which may perhaps be considered only as a peculiar section of the former. 



* I have good reason to believe that Deshayes' uumljer of species of Si/tidosmya from the Paris basLu musi. 

 be somewhat reduced. 



t Tryou quotes iu his catalogue 108 species. 



