56 Transactions of the Royal Microscopical Society. 



margins of all the plates are brought together the anterior surface of 

 the entire sucker is rendered convex, and so becomes detached from 

 the body to which it was fixed, whereas, when the posterior margins 

 are separated, the front surface of the sucker becomes concave, and 

 the marginal spines grasp like claws any inequalities of the body to 

 which they are applied. 



The ring, which is described as a single plate, I have always 

 found to consist of separate plates, equal in number to the seg- 

 ments of the rosette ; they are, however, most frequently arranged 

 in many corresponding sets, one beneath the other. In all cases 

 the extremities of the plates overlap one another. 



