SOLENACEA. MOLLUSCA. PANOP-EA. 37 



jection corresponding to each fissure of the epidermis ; the 

 cartilage-support instead of being arched is forked, and the hinder 

 branch is directed obliquely forwards, extending half way to the 

 anterior margin ; the epidermis is always of a very dark brown 

 or tar-color, marked with fifteen to twenty radiating lines ; the 

 projecting margin is slashed as in the other species, but the angles 

 of the lobes are not rounded, their edges have a thinned, crimped 

 margin, and are usually rolled back. 



Chelsea Beach is the only locality in Massachusetts, that I know of, 

 where this species has been found. A very large and perfect speci- 

 men was found there by Mr. J. P. Couthouy, and is now in the cabinet 

 of the Boston Society of Natural History. Colonel Totten found it in 

 considerable numbers in the vicinity of Newport. 



Only two other species of this genus have been described ; the 

 S. Mediterranea from the Mediterranean, which is distinguished from 

 all the others by wanting the callous supports of the cartilage, and the 

 S. australis from New Holland, which has the size and strength of 

 S. borealis, and the color of S. velum. A notch in the hinge margin 

 behind the cartilage is also spoken of, which we do not find in S. bo- 

 realis. It is not a little remarkable that a genus embracing so few 

 species should be so widely distributed. 



GENUS PANOP^A, MENARD. 



Shell equivalve, transverse, unequally gaping at the sides and at 

 the base ; a small, conical tooth on each valve, and a rounded cal- 

 losity at each side to which the ligament is affixed. 



PANOP-E'A ARCTICA. 



Shell oblong, sub-cylindrical, strong, widely gaping at both 

 ends, rounded anteriorly, truncated posteriorly, traversed by two 

 radiating, wave-like ridges, which divide the surface into three 

 nearly equal portions. 



FIGURE 27. 

 State Coll., No. 236. Soc. Cab., No. 1720. 



Glycy'meris arctica, LAM.; An. sans Vert., vi.70. 



Shell thick and strong, oblong, somewhat cylindrical, inequi- 

 lateral, the posterior portion being nearly twice the length of the 



