The anatomy of Lottia gigantea Gray. 3 



shallow cavities in which to rest (Fig. A). It is evident here that the 

 creature remains in the same spot for a long time. 



Fig. A. Lottia gigantea^ natural size, viewed from one side. F foot, Mr mantle 

 edge, T tentacle. 



Lottia feeds by scraping the rocks, and its alimentary canal is 

 usually gorged with diatoms. The length of the radula tube would 

 seem to show that there is considerable wearing oö" of teeth. 



External features. The outside of the Acmaeidce is almost 

 too well known to need mention in this connection. But as Lottia 

 differs in several respects from Acmaea a short description is here 

 appended. The shell varies from oval to elliptical in outline and when 

 oval is broadest toward the posterior part. In specimens of average 

 large size the length of the shell is 55 to 60 mm, by 45 to 50 broad, 

 and 16 or 17 high. The peak is low and is situated well forward, 

 which enables one to recognize the young animals at a glance. The 

 outside of the shell is usually rather uneven from growth lines and 

 faint ridges radiating from the peak. These show more plainly about 

 the margin. The outer surface of the shell is a light brownish, or 

 sometimes green from algae, but the muscle scar and mantle portion 

 of the inner surface are dark rich brown, frequently disposed in zones 

 of different intensity, and all more or less faintly iridescent. The 

 color of the central portion is a dull bluish white varied with 

 brownish. 



The mantle is well developed and broad, bearing a cordon of 

 branchial lappets, which are absent however in front, opposite the 

 opening of the palliai cavity. This recess is situated on the head as 

 in all limpets, and is roofed by the mantle hood. There is a well 

 developed ctenidium on the left side, attached not along one sinus 

 as in the Rhipidoglossa, but by the base, something after the fashion 

 of the chiton gill. This ctenidium, which has two series of lamellae 

 extends diagonally across the head, and when fully relaxed the tip 



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