CYCLAS. 



TESTA tenuis, aequivalvis, subaequilateralis, 

 epidermide olivacea induta, dentibus, cardina- 

 libus minimis in utraque valva duobus diver- 

 gentibus, in altera valva altero bifido, laterali- 

 bus in altera valva binis, subdistantibus? 

 subelongatis, in altera quatuor, duobus vere 

 perexiguis; impressionibus muscularibus dua- 

 bus, lateralibus, ovatis, impressione musculari 

 pallii sinu nullo. Ligamentum externum^ tenue. 



The Genus Cyclas as first established by Bruguiere includes 

 the two Lamarckian genera Cyrena and Cyclds, which 

 appear to us to have been separated upon rather in- 

 sufficient grounds, though we have already expressed our 

 opinion that such separation may be convenient. The 

 principal difference consists in the thinness of the Cyclades, 

 whereas the Cyrence are comparatively thick and solid. 

 We have already shown how little dependence should be 

 placed upon the erosion of the umboncs either as a 

 generic or a specific character, the thicker individuals 

 being constantly more eroded than the thinner, the Cyclades 

 being very thin are consequently nearly if not quite free 

 from erosion. 



Shell thin, equivalve, generally nearly equilateral, 

 covered with a thin olive green epidermis; there are two 

 very minute diverging hinge teeth in each valve, one of 

 which is double in one valve ; the lateral teeth are rather 

 distant and somewhat elongated, placed on each side of 

 the hinge, of these there are two in one valve and four 

 in the other, two of these latter are, however, very small. 

 The muscular impressions are two in each valve, they are 

 lateral and ovate, that of the mantle is entire without any 

 sinus. Ligament external, slender. 



