Mr. Vigors on some new subjects of Zoology. 409 



falcate they are thin and hooked at the extremity, and in P. 

 crispata they are thin and nearly cylindrical ; but they always 

 keep their incurved form, and their extremity is always placed 

 obliquely, that is, with their anterior portion nearer the centre of 

 the shell. 



To each of these processes there is attached a muscle, which was 

 pointed out to me by my friend, Mr. James Sowerby, and which 

 arises from the foot of the animal ; I agree with him in thinking 

 it must greatly assist them in boring, as by withdrawing the centre 

 of the expanded disk of the foot, the animal, by the pressure of 

 the atmosphere, will be strongly attached to the rock, and thus 

 be furnished wilh a fulcrum to rasp away the surrounding medium, 

 by means of a semirotatory motion, which would be produced by 

 the alternate action of these muscles. 



From the want of specimens preserved in spirits, I have not 

 been able to determine accurately the precise direction and point 

 of origin of this muscle ; nor have I had an opportunity of ex- 

 amining the animals in their natural habitations. The above con- 

 clusion is greatly supported, first by the peculiar form of the end 

 of the foot, of all the species of this family, which alone appears 

 to bore by means of rasping ; and secondly by the oblique posi- 

 tion of the end of the falciform process to the back of which the 

 muscle is attached. ' 



Art. LI. Descriptions of some rare, interesting, or hitherto 

 uncharacterized subjects of Zoology; by N. A. Vigors, 

 jun. Esq. M.A. F.L.S. With Figures by J ames De 

 Carle Sowerby, Esq. F.L.S. 



The number of subjects m every class of zoology which have 

 hitherto remained undescribed in our cabinets has long been a 

 reproach to this country ; and any attempt to remove it by charac- 

 terizing a portion, however limited, of our hidden treasures, needs 

 no apology or preamble. It is my intention to give descriptions 



