134 MYTILID.E. 



in C. rhombea, owing to the greater thickness of the inner coat 

 of nacre. L. 0-15. B. 0-12. 



HABITAT : Coasts of Yorkshire, Northumberland, An- 

 trim, and Scotland from the Clyde district and Firth of 

 Forth north to the Shetlands, in gravelly sand from 3 

 to 70 fathoms. It appears to be gregarious. Post- 

 glacial deposit at Elie, Fifeshire (Rev. T. Brown). It 

 inhabits the seas of Scandinavia, Iceland, Greenland, 

 and New England, occurring at various depths from 

 low-water to 150 fathoms. 



This exquisite gem of a mollusk is hardy and active. 

 Not being able to examine living specimens at the time 

 they were taken, I picked out a few from a small heap 

 of dredged sand, which had been lying on a pathway for 

 two days, exposed to continual rain and partly trodden 

 underfoot. After keeping them eighteen hours in a 

 small glass vessel of sea- water, they revived and were 

 alive for many days, the water being occasionally re- 

 newed. While crawling about, they sometimes carried 

 the shell erect with the beaks in front, but more fre- 

 quently in a slanting position. They seemed fond of 

 getting to the surface of the water, when the Crenella 

 would spin with its foot a single pellucid thread, which 

 it fixed to the side of the vessel, and it would hang (like 

 a Sphterium) for hours thus suspended, the beaks of the 

 shell being undermost. The shell being nearly trans- 

 parent during the lifetime of the animal, the green liver 

 is distinctly seen through it, occupying the umbonal 

 region. The foot-stalk or pedicle is semicylindrical, 

 and becomes twisted if the animal is placed on the wrong 

 side. The creeping-disk or lobe is very flexible and in 

 some degree extensile. It is half as broad again as the 

 stalk, and proportionally thicker. A dusky line runs 

 down the middle of the stalk, apparently showing the 



