434 NEW GENUS AND SOME NEW SPECIES 



Anterior cicatrices distinct ; posterior cicatrices also distinct ; 

 the smaller one being placed against the termination of the 

 lateral tooth ; dorsal cicatrices situated on the under part of 

 the cardinal tooth, very perceptible ; cavity of the beaks deep 

 and sub-angular; nacre white, pearly, and iridescent, rarely 

 tinted with rose in the centre. 



Remarks. — This beautiful little shell is generally an inch 

 long, rarely two. It is common in our cabinets, and has 

 been considered the " rotundata" of Lamarck. I am induced, 

 however, to think it different from our shell, as the circulus 

 never possesses the fold mentioned in that eminent concholo- 

 gist's very short description. The two colours disposed in so 

 peculiar a manner in the epidermis are not mentioned by 

 him. It differs also greatly in size. I have seen some hun- 

 dreds, the largest of which was two inches in breadth. The 

 " rolundata" is 78 millimetres; and its habitat is unknown. 



The margin of the circulus is more perfectly round than 

 any other species; it is sometimes disposed to be subangular 

 posteriorly. The division of the colour on the umbonial 

 slope is very peculiar. When the posterior slope is looked 

 on, this view of the shell is heart shaped, and the dark brown 

 colour is seen entirely to surround the light yellow brown. 

 The epidermis is more satin-like than any other species, and 

 the teeth are peculiarly disposed to be double. In form it 

 approaches the " torsa" more closely than any other species. 



7. Unio JVIulti-radiatus. Plate IX. fig. 15. 



Testa ellipticd, incequilaterali, vcntricosa, multi-radiald ; valvulis te- 

 uuibus ; natibus prominulis ; Jentibus cardinalibus erectis, et in valvu- 

 lis ambabus duplicibus ; lateralibus lamelliformibus et abruptis ; mar- 

 garita cceruleo-albd. 



Shell elliptical, inequilateral, vcntricose, much rayed; valves thin; 

 beaks rather prominent; cardinal teeth erect and double in both valves ; 

 lateral teeth lamelltf'orm and abrupt; nacre bluish white. 



