27<> THE NATURAL HISTORY OF 



ORDER III. EQUIVALVES. 



DIVISION II. EDENTATE, OR TOOTHLESS. 



GENUS.— MYTILUS, OR THE MUSCLE* 



SPECIES DISCOVERED IN THE ARCTIC SEAS. 



SPECIES I. 



MYTILUS RUGOSUS vel ARCTICUS, 



OR 



THE POLAR MUSCLE. 



The shell of this species is rhombic, brittle, rugged, and 

 rounded at the ends. It inhabits the northern seas and 

 lakes. It was found by Captain Phipps in Smeerenberg 

 Harbour. Great numbers of them usually are found lodged 

 in limestone, each in a separate apartment, with apertures 

 which are too small for the shell to pass through without 

 breaking the stone. The shell is about an inch and a 

 quarter long, and in breadth about half its length ; its 

 colour is of a dirty grey, and within is half blue and half 

 white, marked with very small longitudinal striae, crossing 

 the transverse wrinkles. 



SPECIES II. 



MYTILUS FABA, OR YELLOW MUSCLE. 



The shell of this species is oval, yellow, striate, with a 

 cremulate margin. It inhabits the Greenland seas, attach- 

 ing itself to the rocks, by a bronzed byssus or beard. 



* Genus xlvi. Brewster's Conchology. 



