OV SOUTHERN INDIA. 37 



stand near Necera, but the tooth in each valve would recall EucJiaris. Whether the 

 anterior laminar process occurs in both valves and whether it is for the purpose of 

 supporting the cartilage, which seems likely, has yet to be satisfactorily determined. 

 Lycett does not mention this genus in the large work on the fossil MoUusca 

 of the Great Oolite. 



7. Corbulamella, Meek and Hayden, 1857 (Proc. Acad. Nat. Sc, Phil., p.l 42). 

 Shell sub-triangular, sub-globose, inequivalve, the right valve being more ventricose 

 than the left ; beaks nearly central ; hinge with one cardinal tooth in each valve, 

 apparently very similarly arranged in position to that of Qorbula, but the existence 

 of an internal cartilage has not as yet been satisfactorily proved ; anterior muscular 

 impression rather indistinct, posterior on a special raised or projecting plate ; pallial 

 impression scarcely sinuated posteriorly. 



This is proposed for a cretaceous species from Nebraska, C. gregarea ; it resem- 

 bles Cardilia in form, but is distinguished from this by the irregularity of the valves. 



8. Spheniopsis, Sandberger, 1863, (Conch, des Mainzer Tertiger-beckens, 

 p. 289). Shell sub-trigonal, compressed, equivalve, posteriorly rostrate and slightly 

 gaping ; hinge of right valve with an anterior cardinal tooth, and a deep cartilage-pit 

 behind it, a long laminar tooth runs along the areal margin ; left valve edentulous, 

 only provided with a cartilage-pit ; pallial sinus deep. This genus is based upon a 

 tertiary species, which is an intermediate form between Corbula and BUnomya (a sub- 

 genus of NecBTo), It may also be considered to represent a compressed Poromya. 

 Sandberger calls the shell equivalve, but the presence of the posterior laminar 

 tooth in the right valve seems to me to indicate that the left valve must be a little 

 smaller, in order to fit to the right one without possessing a special double tooth. 

 Necera jugosa^ Wood, (English Crag. Moll., vol. ii, p. 272,) very likely belongs to 

 Spheniopsis, 



9. Necera, Gray, 1834. Shell inflated, thin, posteriorly prolonged and gaping, 

 right valve somewhat smaller ; one cardinal tooth in each valve, spoon-shaped for the 

 purpose of supporting the cartilage, occasionally with a minute tooth in front of it, 

 a lateral posterior tooth, much larger and more distinct in the right valve than in 

 the left ; ossicle distinct, small ; ligament external, very small, situated just behind 

 the beaks. The thin, usually finely lamellar structure, and the inflated form of the 

 shells belonging to this genus, are very characteristic. H. and A. Adams place it 

 in the Anatinid^, though judging from the form of the shell, being in many 

 respects similar to that of Corbula, and also from the form of the small foot and the 

 short siphons of the animal, there can be little doubt that Deshayes' classification 

 near Sphenia and Corbula, etc., is the more correct one. Almost the only character 

 which some species of the genus have in common with the Anatinidje is the presence 

 of a small ossicle at the cartilage, but as all the Anatinid^ do not possess the same, 

 its presence cannot be regarded as an exclusive character of that family. Nearly 

 all the species of Necera, living in deep water, possess a thin shell, often very finely 

 punctated ; only very few, being more littoral in their habits, have a rather solid and 

 opaque shell, like My a or Thracia, 



K 



