392 



GEOLOGY OF THE SECOND DISTRICT. 



SO detacliing llic stony matter from the inferior surface, as to sliow its legs, or the divisions 

 of its abdomen. 



From all tlie facts which liave been disclosed in relation to these animals, I see no objection 

 to placing them in one family, and considering the recent crustacean which I have figured as 

 a representative of the ancient race. Some difference in organization may be found, yet the 

 general form and some of the habits are so nearly alike, that in considering them all as one 

 familv, our error will be but tritling. In conclusion, I would rcinark that one important duty 

 yet remains for geologists and naturalists, namely, to compare, more carefully than they have 

 yet done, fossil with living bodies. 



Havino- stated the principal facts in relation to the localities of the crustaceans of the Tren- 

 ton period, I shall now introduce the following cuts illustrative of the univalves which have 

 been discovered in this rock. 



101. 



1. Trocholites ammonius. 



2. Plcurotomaria lenticularis. 



3. Subulites elongata. 



4. Cyrtoceras filosum. 



5. Bcllerophon punctifrons. 

 G. Bellerophon bilobatus. 



No. 1, is a rare fossil in the trenton ; it has been found in the Mohawk valley, but it has 

 not fallen under my notice in the Second district. 



No. 2, is quite abundant at Watertown, and is common in tlie sub-crystalline grey variety 

 of this rock. This is a large individual. 



Nos. 2 and 3 (fig. 102, ]>. 303), are the same species, and are drawn of the usual size of the 

 animal. 



