SEA- WEED LIMPETS. 103 



This shell may be distinguished by the position of 

 the apex, which is situated very near one end, 

 making nearly all the slope come upon one side like 

 the roof of an old-fashioned farm-house. The ribs on 

 the slope of the shell are prominent but irregular. 

 The outside is gray or mottled, and the inside has 

 varying amounts of brown and white. This shell is 

 high-arched, but it seldom grows to the length of an 

 inch. 



Besides these Limpets which may be gathered from 

 the rocks, there are several species which are found 

 upon the stems of sea-weeds. The largest of these 

 Sea-weed Limpets, as they are called, is named 

 Nacella instabilis, Glk., Na-sel'-la in-stab'-i-lis. The 

 shell is limpet-shaped, narrow, compressed at the 

 sides, smooth, brown on the outside and white within. 

 Its length is three-fourths of an inch and its breadth 

 is a little less. 



Nacella incessa, Hds., in-ces'-sa, Fig. 91. This is 



the common species, and may be found 



on the flat central ribbons of the olive 



green seaweeds, which are so conspicuous 



near the rocky shore. The sides of the 



shell are flattened and nearly smooth, 



Fig91 - and the apex is rounded. The shell is 



of a dark brown color throughout, and looks as if it 



were made of horn. It is about half an inch long 



and is of the same height. 



Two other species I will briefly describe. The first 

 is named Nacella depicta, Gld., on account of its 

 painted appearance. Shell very narrow, with straight, 

 flat sides. White, with fine brown stripes radiating 

 from the apex. One-fourth to one-half an inch in 

 length. Southern; on grass at low tide. 



