OF SOUTHEEN INDIA. 39 



the cartilage. Ohenu (Man. ii, p. 33,) states, that there are three muscular impres- 

 sions present, a posterior oblong, an anterior transverse, and a third small one 

 between the latter and the hinge. 



This genus, which, by the binge of its shell and by the long siphons of the 

 animal, is well distinguished from Corhula, includes a number of estuary shells from 

 South America ; it is in many respects intermediate between Necera and Corbulo- 

 mya ; it is also sparingly represented in our eastern seas, the Philipines, and the 

 Bay of Bengal. 



12. Corbulomya, Nyst., 1846, (Coquill. foss. de la Belgique, p. 59). Shell 

 transversally ovate, closed on both ends ; right valve larger, with one cardinal tooth 

 in front of a cartilage-pit ; left valve with two distant teeth, the posterior of which 

 supports the ligament ; pallial sinus very small or obsolete. 



This genus has been proposed for fossil species, which appear to be rather 

 numerous in the tertiary formation, but none of them has as yet been sufficiently 

 made known from mesozoic beds, though very likely a number of the small Myacites, 

 or Anoplophorce, and others, will be shown to belong to it. A recent species known 

 as Cor6. mediterranea occurs in the European seas. 



The genus closely approaches in the dentition of its hinge Eucharis, but in 

 this one the anterior tooth of the left valve is much stronger than the posterior. 



13. Cryptomya, Conrad, 184.8. Shell transversally oblong, rather compressed, 

 generally sub-equilateral, slightly gaping on both ends, more so posteriorly ; hinge of 

 both valves with a spoon-shaped cardinal process, receiving the cartilage, the process 

 of the right valve being usually somewhat larger, and having in front a small tooth 

 or a thin ridge ; pallial sinus small or none. The surface of the valves is often 

 decussately striated, and such species appear to form a good passage to the next 

 genus. 



14. Tugonia, Gray, 1842. Shell oval, inflated, with the beaks directed back- 

 wards, widely gaping posteriorly, equivalve ; hinge consisting of a spoon-shaped, 

 cardinal process in each valve with a small posterior denticle ; cartilage internal in 

 the process, ligament external, short, partially extending over the beaks ; pallial 

 sinus very small or wanting. There are only a few recent and tertiary species of 

 this genus known ; none have been as yet found in cretaceous rocks. This genus 

 could be equally well placed in the Anatinidjei but it seems to be connected with 

 Mya through the next one. 



15. Flatyodon, C onrad, 1837. Shell elongated, inflated, solid, with the surface 

 cancellated, posteriorly widely gaping, equivalve, tooth in the right valve very broad, 

 anteriorly with a short ridge, the beak of the left valve excavated for the reception 

 of the right one. The type of this genus is Platyodon cancellatus, the only species 

 as yet known ; the animal is said to have at the end of the siphons four testaceous 

 appendages ; by the structure of its shell, equal valves and the form of the beaks, 

 this form seems deserving a distinct generic name. 



