64 DUBLDT NATXJEAL HISTORY SOCIETY. 



tures on the upper surface of the spines, prolonged into tubes, similar in 

 some instances to those of the Haliotidao, and of these tubes the anterior 

 remain open, while the posterior tubes are gradually closed up. We 

 thus see that while Euomphalus, in its ordinary forms, belongs to the 

 group of low-spined Trochidae, yet that it keeps up the most intimate 

 relations with Pleurotomaria and Haliotis ; so far as mere form is con- 

 cerned, Euomphalus cannot be separated from Cirrus; and yet the 

 structure and habits of the animals inhabiting the two kinds of shells 

 must have been very diiferent, as the breathing apparatus indicated by 

 the short tubes of Cirrus was of a totally different character, from that 

 of Euomphalus. 



If we were to judge by mere form, there would be the greatest dif- 

 ficulty in separating Cyprina from Yenus ; and yet even a palgeontolo- 

 gist could tell that they differed, by the impression of the mantle on the 

 shell. 



But, although I admit that slight differences, where they indicate 

 physiological structure, are and ought to be of importance, I may be 

 allowed to doubt if they are as important to the geologist as to the zoo- 

 logist. It must not be forgotten that, although Geology throws much 

 light on some branches of Natural History, in filling up lacunae in our 

 knowledge, yet that our knowledge of the habits and structure of any 

 fossil, however perfect, is at best extremely small, compared with our 

 acquaintance with living forms. It is not, therefore, necessary to be 

 so precise in pur subdi\dsions of fossil as of recent genera, and no greater 

 injury can be done to the science of Geology than has been, by the use- 

 less multiplication of worthless names, founded on distinctions which are 

 necessarily trifling, because our knowledge of the true structure of the 

 fossil is exceedingly imperfect. 



In the present case (Euomphalus or Solarium), speaking simply as 

 a geologist, it appears to me that all useful purposes will be served by 

 retaining the same generic name for all the varieties, and dividing the 

 genus into three subdivisions, as follows : — 



EUOMPHALrS. 



Type A. — Flat-spu-ed ; provided with breathing tubes like the Halio- 

 tidae. Type species : — 



1. Euomphalus cristatus. 



2. Euomphalus Goldfussi. 



Type B. — Raised spire ; provided with a deep slit in the exterior 

 lip, and a sinus band on the shell. Type species : — 



1. Euomphalus Eeginae (Haughton). 



Type C. — Ordinary flat spired, smooth forms of Euomphalus. Type 

 species : — 



1 . Euomphalus pentangulatus. 



2. Euomphalus pugilis. 



