16 TEREBRATULID^. 



hydrographical range extends from Spitzbergeu to Sicily; 

 and the variety is not uncommon on the coasts of Nor- 

 way and North America. Mr. Arthur Adams has lately 

 dredged the typical form in the seas of Japan, at the 

 depths of 26, 55, and 63 fathoms. He considers T. Ja- 

 ponica to be a distinct species. I have a monstrosity 

 which is deeply cleft in the middle, so as to form two 

 lobes of unequal size and height ; and other specimens 

 also are slightly distorted in the same way. 



The brachial cirri are set on the muscular stem like 

 the teeth of a comb, and when in action they bend for- 

 ward in a most graceful manner. The pallial tentacles 

 are also continually moving, and sometimes curl at the 

 point like a crosier. When the shell is closed during 

 the lifetime of the animal, these tentacles are still visi- 

 ble outside the edge of the shell, presenting the same 

 appearance as in Anomia. Sometimes the upper valve 

 is laden with a mass of barnacles and Serpulcs. The 

 shells of young specimens are, of course, more strongly 

 ribbed or striate than those of the adult ; and the lower 

 valve is eared. The fry, however, are perfectly smooth, 

 and much longer in proportion than the adult; and 

 they have a spoon-shaped, entire, and prominent beak. 

 Owing to the shell being so thin and nearly transparent, 

 the tiny arms are distinctly perceptible on the outside. 

 In the early stages of growth the skeleton is not com- 

 plete or annular, and it then somewhat resembles the 

 scythe-shaped processes of T. cranium. 



The Anomia retusa of Linne and A. aurita of Gual- 

 tieri, as well as the T. nucleus and T. pubescens of O. F. 

 Miiller, are synonyms of this species. The last-men- 

 tioned name originated in a coat of downy sponge, which 

 not unfrequently covers the shell, and was suspected 

 by the Danish zoologist to be merely a parasitic growth. 



