46 CONTRIBUTIONS 



revoluta (Sowerby), but seems to differ in the angle of the 

 posterior part. 



C. Murchisonil Plate 1. Fig. 13. 



Description. She'll much inflated, triangular, subbian- 

 gulate behind, nearly equilateral, very inequivalve ; right 

 valve covered with regular, large, transverse ribs, which 

 terminate at the sharp carina of the umbonial slope ; left 

 valve smooth or slightly wrinkled, with two or three obscure 

 ribs passing from the beak to the basal margin, and a linear 

 umbonial slope, posterior to which there is a deep fold ; 

 beaks very large and incurved ; tooth and pit of the left 

 valve large ; posterior slope truncate, furnished with a dou- 

 ble carina on the right valve and a single carina and fold 

 on the left. Cicatrices not distinctly impressed ; cavity 

 of the beaks very deep. 

 Diam. .3, Length .5, Breadth .6, of an inch. 



Observations. I have peculiar pleasure in dedicating this 

 curious and beautiful species to the late president of the 

 Geological Society of London, who, by his numerous and 

 excellent papers on geology, has eminently contributed to 

 promote a knowledge of his favourite science. The Mur- 

 chisonii is remarkable for the great disparity of the size of 

 its valves, and their total dissimilarity. It has some re- 

 semblance to the elegans (Sowerby). 



C. gibbosa. Plate 1. Fig. 14. 



Description. Shell very transverse, somewhat inflated, 

 nearly equilateral, very inequivalve, on the right valve 



