MOLLUSCA — GASTROPODS 



249 



This is an extinct genus exceedingly abundant in the Silurian 

 and Devonian. 



Tentaculites, HyoUthes, Conularia, etc., are genera of prob- 

 lematic relationship occurring abundantly in the Paleozoic. 



Fig. 109. — Tentaculites gyracanthus 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 

 Mollusca, 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 they are undoubtedly most closely akin to the 

 Gastropoda among classes of living mollusks. 



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

 ring-like ornamentation. 



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

 raised into a distinct class ? 



