394 



GEOLOGY OF THE SECOND DISTRICT. 



the moutii ; but in a single and much larger specimen, it appeared that the mouth was 

 remarkably expanded and wide, so much so as to be apparently out of proportion to the rest 

 of the animal. 



1. Inachus undalus. 



2, edge view. 



This remarkable fossil is found at Watertown, in the black limestone. It is rare. Casts 

 sometimes occur which are smooth. 



The following bivalves may be considered as characteristic of the Trenton limestone : 



Strophomcna scncea. 



2 3 



2. Orthis pcclinella. 3. Orlliis strialul.1. 



Nos. 1 and 2, but more particularly the latter, abound at numerous localities in this county. 

 No. 3. This is probably as constant at all the localities in the trenton rock which have been 

 examined, as any fossil which I have hitherto observed. 



