MOLLUSCA — GASTROPODS 



249 



This is an extinct genus exceedingly abundant in the Silurian 

 and Devonian. 



TentacuHtes, Hyolithes, Conuiaria, etc., are genera of prob- 

 lematic relationship occurring abundantly in the Paleozoic. 



B 



Fig. log. — Tentaculites gyr acanthus Eaton. A straight gastropod (conularid) from 

 the Upper Silurian of New York. A, block of limestone showing their abundance 

 (natural size). B, two individual shells (X 4), the smaller one has been slightly 

 crushed. (After Hall.) 



They are often raised into a distinct class of the phylum 

 MoUusca, the Conularida. Though the occasional presence of 

 transverse septa has somewhat suggested relationship with the 

 Cephalopoda, still their shell is most similar to that of Clio, 

 and hence thev are undoubtedlv most closelv akin to the 

 .Gastropoda among classes of living mollusks. 



1. Sketch side view, noting the long, uncoiled tube with its 

 ring-Uke ornamentation. 



2. Why is this shell, and others of similar structure, often 

 raised into a distinct class ? 



