OP SOUTHERN INDIA. 53 



14. Lutraria, Lamarck, 1799. Shell oval, rather comi^ressecl, posterior gape 

 moderate, cardinal teeth small, anterior lateral elongated, prominent, posterior 

 obsolete, or nearly so; ligament attached on the inner side of the margin just 

 behind the beaks, not much visible externally; pallial sinus deep. 



15. Standella, Gray, 1837, Shell ovate, slightly tumid, hinge with the lateral 

 teeth very close to the cartilage-pit thin, obliquely diverging, ligament sub-external, 

 marginal, not distinctly separated from the cartilage. This is by no means equally 

 distinct from Lutraria, as is, for instance, Zenatia or Vanganella, and may better 

 be regarded only as a sub-genus of the former. 



V^a. The species separated under the sub-generic name of Merope, H. and 

 A. Adams, have a somewhat thinner shell and a radiately striated or ribbed surface; 

 these ribbed species form a transition to the next. 



155. Mactromeris. Conrad refers to this sub-genus Standella ovalis, Gould, St, 

 ovata, Gray, and five others (see Cat. of Mactrid^, in vol. iii. of the Amer. Jour, of 

 Conchology, p. 45). 



' 16. Eastonia, Gray, 1849. Shell oval, ventricose, thick, radiately ribbed ; hinge 

 with the cardinal teeth of the left valve thin, laminar, narrowly notched ; anterior 

 lateral nearly perpendicular, and in front of it, or rather in its horizontal prolongation, 

 there is another small tooth present; posterior lateral teeth long; ligament sub- 

 external; not separated from the cartilage, supported in the right valve by a distinct 

 rib. 



The tertiary fossil form^ which has been identified with the only recent species, 

 M rugosa, Chem., has the groove and small tooth in front of the anterior lateral 

 tooth very distinct, and the cardinal tooth not very strong (see Homes, fossileMoU. 

 des Tertiser-beckens, Wien, vol. ii, pi. 5, fig. 4). The posterior lateral is specially 

 long and very much approaches that of the mactein^. 



h\ Suh-famili/.-^MACTBINM 



The arrangement of the genera is according to the size of the lateral teeth. 



17. JSarvella^ Gray, 1849. Shell sub-trigonal, rather thin, posterior slope 

 keeled ; cardinal teeth small, lateral teeth close to the cardinal, short ; hinge margin 

 double, liganient marginal, separated from the cartilage by a shelly lamina. The 

 only species is _H". elegans from Florida. The two following sub-genera agree in 

 form of the shell with JSarvella, but show slight distinctions in the form of the 

 hinge-teeth. 



iTa. Mactrella, Gray, 1849. Shell rather long, hinge with the hinder lateral 

 teeth very small, sometimes almost obsolete, anterior distinct and distant from the 

 small cardinal. The type of the genus is Mact. alata^ Spongier, or M, carinata^ 

 Lam. 



175. Mactrinula, Gray, 1849. Shell with the cardinal teeth short, lateral 

 close to them, but much more elongated than in the last. The species of Mactrinula 

 can only be considered as slightly differing from Sarvella ; there is no sufficiently 







