OP SOUTHERN INDIA. 305 



D'Orbiuii}' referred (iu Prod, ii, p. 79,) all the species (seven) described by Sower by* from the 

 Wealden beds of England to his lower Neoeomien, but at the time of writing he does not appear 

 to have been acquainted with Bunker's " Monographie der Nordeutschen Wealdenbilduno-," &c. 

 Geologists have up to the present not agreed upon the classification of the Wealden deposits, but it 

 seems more conformable with the facts observed iu nature, that the Wealden locally indicates 

 the close of the Jurassic period, than the beginning of a fresh series of marine deposits. ' 



XXXI. Family —MVTBLIBJE. 



The labial palps of the animals are stated by H. and A. Adams to be laro-e, 

 oval, attached by their straight edges without any free points, as in TInionid^ ; 

 the mantle-lobes united posteriorly, and prolonged into two short, unequal siphonal 

 tubes ; gills large, nearly equal, united to the body ; the foot large, thick, compressed, 

 tongue-shaped, angular iu front. The shells are sub-quadraugular or elongated, 

 often with wing-like extended upper margins, the hinge being straio-ht with 

 numerous denticulations, or they are oval, and then generally rather solid, resem- 

 bling Triyonia, to which the hinge-teeth also bear some relation, althouo-h in their 

 distribution they are more similar to those of IJnio. 



Looking at the above noted characters of the shells referred to this family, as 

 compai'ed with the Unionidje, one cannot hesitate in accepting H. and A. Adams' 

 classification, but if the statement regarding the differences pointed out between 

 them and the last family is not generally correct, the distinction of the two families 

 can hardly be retained. I have unfortunately no materials whatever to test the 

 accuracy of the statement, and therefore accept the family as it stands in H. and 

 A. Adams' work. The species are mostly African and South American. I do not 

 know any fossil species belonging to it. 



1. Mutela, Scopoli, 1777, Clridina, Lam., 1819). Shell very elongated, 

 inequilateral, the anterior portion being much shorter than the posterior, thin; 

 hinge line thin, nearly straight, as long or very nearly as long as the shell, cre- 

 nulated or tuberculated along its entire length or only partially ; type, 31. elongata, 

 Sow., from the Senegal. Hanley describes in Reeve's Conch. Icon., vol. xvi, 

 five species, all from Africa. H. and A. Adams accept for 31. NiloUca, r6r., 

 as type, Swainson's name CalUscapha as sub-genus, that species having the hinge 

 margin crenated only partially near the beaks. 



2. Pleiodon, Conrad, 1835. Shell sub-trapezoidal or elongated, rather solid, 

 inequilateral, the anterior side being somewhat shorter, hinge line flattened, some- 

 what shorter than the shell, and with numerous irregular plications or teeth ; 

 surface covered with a smooth thick epidermis; type, PL ovatus, Swains. Hanley 

 (Reeve's Conch, Icon., vol. xvi,) describes only one other species, Fl. Spekei, 

 Woodw. ; both are from Central Africa 



3. 8patha, Lea, 1838. Shell elongated, thin, inequilateral, with the upper 

 posterior edge somewhat expanded; hinge line slightly arcuate, toothless; type, 

 Sp. riibens. Lam., from the Senegal; two other species are also from Africa. 



* See liis Min. Couch, and Tmns., Geol. Sue, London, 2iid series, vol. iv. 



