OF SOUTHERN INDIA. 301 



so often made an object of complaint by couchologists that I do not need 

 to repeat it here. None of the sub-divisions as yet suggested can be called 

 satisfactory, and I am constrained to say that the attempts to make them 

 so are not likely to be very successful. The sub-divisions, if they were to 

 be of any use and convenience for the grouping of these shells, must principally 

 be based upon the mere external form or shape, and the general modification 

 of the hinge-teeth as dependent on that form. The form, or rather the posi- 

 tion of the supplemeutaiy anterior muscular scar, seems in some groups to 

 remain tolerably constant. H. and A. Adams (Genera ii, p. 490,) recognise the 

 following sub-genera — Bariosta, Haf., Naidea, Swains., Obovcwia, Raf., Nida, 

 Swains., Myridella, Swains., LampsiUs, Raf., Canthyria, Swains, Irldea, Swains., 

 Rotundaria, Raf., Quadrula, Raf., Diplodon, Spix, Di]S)iomia, Ag., Plagiodoii (1. cit., 

 p. 651), and Iletaptera, Raf. Conrad quotes from the eocene deposits of North 

 America a sub-genus Uniomeris (vide Smiths. Misc. Coll., No. 200, 18G0, p. 5). 

 A peculiar fossil form will also be indicated in the list of cretaceous species. 



4. Margaritana* Schuhm., 1817. Shell oblong, moderately compressed; 

 hinge with a single erect tubercular anterior (cardinal) tooth in the right valve, 

 double in the left, the anterior half being smaller than the posterior, which is often 

 denticulated or slightly rugose, but all the teeth are covered with enamel like 

 the rest of the interior of the shell ; posterior hinge-teeth more or less obsolete. 

 Type, II. margaritifera, Linn. 



H. and A. Adams regard the following as sub-genera of the above: — Alas- 

 modonta, Say, f ? = ElasmodonJ, Complanaria, Swains, and Uuiopsis, Swains., 

 ( = Calceola, Swains, non Lam.). Ilargaritana differs from Unio by the want of 

 the posterior hinge-teeth ; they are not developed in any of the known species, and 

 if indicated it is only by a peculiar thickening of the hinge margin, very distinct 

 from what is seen in Uiilo proper. 



5. Monocomhjlcea, d'Orb., 1835. Shell sub-rotundate or oblong, hinge-teeth 

 represented by one anterior tooth in each valve, the one in the right valve being 

 under or posterior to the beak, the other in the left valve anterior to it ; the teeth 

 are elongated in the direction of the hinge margin, and the region in front of the 

 beaks is bent in and partially filled with the ligament, posterior teeth obsolete ; type, 

 M. Faraquaijana, d'Orb. 



American concholosjists have certainlv not shown less ansietv in the discovery 

 of new genera and species in the Indian regions, than they do in their own 

 country. 



5 a. Gould, in 1814, suggested for some Burmese and Malayan species the 

 name Pseudodon, of which liis Ps. Salwinkums, — bearly distinguishable from 

 Monocondylcea Pegnensls, Anthony, (Am. Journ. Conch., 1865, i, 205, non Viilo 

 Pegnensis, Anthony, also from Burmah) — is atypical species. In this and other 

 allied forms the teeth are quite of the same peculiar character, being more or 



* I do not think that Meusc hen's name i?«^j/;/a has any claim of priofity before Maryantana ; I do nut find 

 that it possessed any restricted sijjuificatiou before the introduction of the latter name. 



