The Key-hole Limpets 



central tooth of the radula is wide. It is by internal characters 

 proved to belong in the group with Emarginula, which has the 

 apex usually closed, with the slit between it and the margin. 

 The little "chopped off" end of the inner rim of the hole is the 

 sign by which shells of this genus are best recognised. 



G. alternata. Say, is the common key-hole limpet of the 

 Atlantic coasts. It is an inch or more in length, with a much 

 elevated peak, and a very finely and distinctly ribbed surface. 

 The ground colour varies from pale dingy yellow to grayish brown, 

 and there are usually eight dark radiating stripes ornamenting 

 the shell. The lining is white, with a deep pit back of the apical 

 key-hole. 



Habitat. — Chesapeake Bay to the West Indies. 



The Rough Key-hole Limpet (G. aspera, Eschs.), a peaked 

 key-hole limpet of the Pacific coast, is the largest species 

 of its genus; the oval shell is over two inches long. Its dirty 

 white exterior is radially streaked with regularly widening dark 

 bands, and ridges that have thin, sharp blades. The apical hole 

 is almost round, and very thick-walled. 



Habitat. — Sitka to Monterey Bay. 



THE SLIT LIMPETS 



Genus EMARGINULA, Lam. 



Shell oval, conical, like a clown's pointed cap, with narrow 

 vertical slit in from the front margin. Cabinet specimens, how- 

 ever small, can be easily traced to their proper genus by their 

 limpet shape and this peculiar slit. The few North American 

 species are found on the Florida Keys. 



Genus SUBEMARGINULA, Blainv. 



Shell roundish oval ; apex high, near middle, curved back- 

 ward; surface radially ribbed; anal slit a short marginal notch, 

 with internal groove leading toward apex. Southern Florida 

 has two species. The genus is well represented in the West Indies, 

 and in all the archipelagoes of tropical seas. 



S. RoUandii, Fisch., is a little shell with radiating ribs 



229 



