MOLLUSCA OR UNIVALVES. 231 



genus, and is found plentifully in the Frith of 

 Forth. 



( 97. Pteroceras. — Shell oblong; spire 

 small ; mouth terminated by a 

 rather long canal ; right lip di- 

 lated in the adult into several 

 claws, and having a sinus near 

 the canal ; operculum horny. 

 Animal like the Strombus. — 

 7 species, recent. 



The number of claws varies 

 in different species ; the Pteroceras millipeda 

 has a great many, but they are small; in others 

 they are straight, or nearly so, and smooth; 

 whilst many of them have these appendages 

 very much curved. 



There is much singularity in the growth of 

 these shells, and the appearance they present at 

 various periods is strikingly different. In the 

 young state of the animal the shell has no claws, 

 and these gradually make their appearance, at 

 first in the form of short and open canals, 

 which by degrees assume the length and curve 

 of the adult and completed shell, and eventually 

 Q 4 



