SHELLS WITHOUT CANALS 219 



This species is generally found living where the rocks 

 are seldom covered with water. 



Acnicza scahra^ Nutt., the File Limpet, is usually 

 of a light brown color externally, while the inside is 

 white. Sometimes the external brown is so light that 

 it is almost yellow, while again the surface may be 

 quite dark. The arch of the shell is generally low, 

 like Figure 211, and there are fine, sharp, scaly ridges 

 radiating from the apex, making the shell feel like 

 the surface of a fine-cut hie. Sometimes it is a little 

 difficult to tell a shell of this species from one of 

 A. patina^ but if you can see the animal you will at 

 once decide, for the head and mantle of the former 

 are black, while those of the Plate Limpet are always 

 white. The ordinary length is about an inch, and 

 the low-arched shell is quite thin. Occasionally very 

 aged specimens are found which have lost all their 

 sculpture and have become very thick. They can 

 be told, however, by the white appearance of the 

 interior of the shell, if the fleshy parts have been 

 removed or are lost. 



Acnicza mitra^ Esch., the White 

 Cap, Figure 214, generally lives be- 

 low the tide-mark and is seldom 

 found living, though I have occasion- 

 ally found them at extreme low tide. Fig. 214 

 The shell is pure white, fairly thick, 

 and has a very pleasing appearance. ALmy dead 

 specimens are washed up by the waves, and they 

 always find plenty of admirers. Often the outside 

 of the living shell is covered with a growth of small, 

 hard seaweeds, making it rough or irregular, but 



