206 KELLIIDvE. 



lines of growth : colour yellowish -white : epidermis extremely 

 thin : margins abruptly truncate but rounded at the smaller or 

 posterior end, with an oblique slope to the ventral margin, 

 which is also curved and rather deeply indented for the 

 byssus, very broad, wedge-shaped, and rounded at the anterioi 

 end, and forming an obtuse angle behind : beaks small, blunt, 

 and nearly straight, protruded beyond the dorsal margin ; they 

 are placed very much nearer to the posterior side, which is 

 not one-fourth the size of the other : hinge-line slightly curved, 

 occupying about one-fifth of the circumference : cartilage 

 yellowish-brown and semicylindrical, clasping the hinge-line 

 on the posterior side of the beaks : hinge-plate short and 

 narrow, but strong, not deeply excavated in the middle : teeth 

 triangular and pointed, that on the anterior side in each valve 

 being longer and rather larger than the other ; the teeth in one 

 valve lock into sockets in the other, but not in the correspond- 

 ing valve of every specimen — it apparently being indifferent 

 whether the right or left valve contains the more prominent 

 teeth or the sockets : inside nacreous and glossy, with a plain 

 margin : pallial and muscular scars indistinct, the former being 

 more perceptible than the latter. L. 0*115. B. 0-125. 



Var. Icevis. Shell smooth and destitute of the radiating 

 striae. 



Habitat : On the ventral spines of Spatangus pur- 

 pur eus, and occasionally of Amphidetus ovatus {A. roseus, 

 Forbes), in sandy ground, at depths ranging from 8 to 

 90 fathoms, on every part of our coasts. Capt. Beechey 

 took it alive on the Spatangus in 110-140 fathoms off 

 the Mull of Galloway. The variety is from deep water 

 in Shetland. It is a Coralline Crag species. Loven, 

 Sars, Asbjornsen, M' Andrew, and Malm have recorded 

 it as inhabiting the Scandinavian seas from Finmark 

 southwards, Petit as found in the north of France, and 

 Recluz, Verany, and Mace as Mediterranean. The last- 

 named conchologist informs me that it occurs in the 

 Gulf of Lyons on Cidaris hystrix. Sars mentions that 

 at Naples it attaches itself to Spatangus meridionalis; 

 and Malm says that on the coast of Bohuslan not only 

 S. purpureus and A. ovatus, but also Brissus lyrifer, are 



