92 



SHELLS AND SHELL-FISH. 



links which connected two genera were discovered, the 

 two should be thrown into one. Experience, however, 

 setting aside all other considerations, has long ago con- 

 signed this dogma to oblivion, and has even obliged its 

 warmest advocates to renounce it. Every day, almost^ 

 is bringing before us, — particularly in the invertebrate 

 animals, — not only forms altogether new, but such modi- 

 fications of those we already have in our collections, 

 that in a few years we may fairly anticipate not one in 

 ten of the testaceous genera, now apparently isolated, 

 will remain so ; the links which unite them to others 

 will be discovered ; and thus, had we continued to unite 

 one genus to another in the fashion above adverted to, 

 we should be now fast approaching that simplicity of 

 nomenclature which would class all shells under one 

 genus, — the genus Testacea. It is only by following 

 out a theory of this sort, and seeing to what it would 

 lead in a general and extended application, that we can 

 judge of its philosophic soundness or of its practical 

 utility. 



(80.) AU the types of the Fusince, as will now be 

 shown, have their representatives in the PyrulirKs. 



Analogies of the Fusing and the Pyrulin^. 



Genera of the 



Fusing. 



Hemifusus. 



Fusus. 



Chrysoiomus. 



Lelosfomus. 



Strepsldura. 



Analogies. 



f Trapeziform, or sub-fusiform;? 

 ^ channel short. j 



C Channel remarkably long; the 7 

 \ whorls generally angulated. 3 



Channel moderate. 



f Spire very short ; the basal whorl") 

 large and ventncose. i 



The base of the pillar slightly'^ 

 turned outward, the exterior >• 

 rough and mucronate. j 



Genera of the 



Py RULING. 



Cuma. 



Pyrula. 



Ficula. 



Rapella. 



MyrisUca. 



The first of these resemblances, or that between 

 Hemifusus and Cuma, is obviously an affinity, since the 

 most inexperienced student can perceive that these two 

 groups pass into each other. The greatest elongation 



