24 CANADIAN FOSSILS. 



or ridges, crossed by oblique, straight (or very slightly sinuous) 

 lines of growth. No umbilicus. The mouth rounded, and with 

 an imperfect peritreme. Inner lip thin, closely reflected, and 

 a little concave. 



Trochonema, Salter. 



Trochonema. — Mollusca Gasteropoda. Family Litorinidse. Turbi- 

 nate, thin, of few angular whorls, marked by strong concentric 

 ridges, and crossed by very oblique lines of growth. Umbilicus 

 wide, open. Inner lip thin, scarcely reflected; peritreme com- 

 plete. 



Eunema, Salter. 



Eunema. — Mollusca Gasteropoda. Family Litorinidae. Turbinate 

 thin, of few angular whorls, marked by strong concentric ridges, 

 and crossed by strongly sinuate, prominent, and thread-like lines 

 of growth. Inner lip not reflected j peritreme simple ; mouth 

 rather effuse below ; no umbilicus. 



Loxonema, Phillips. 



Loxonema. — Mollusca Gasteropoda. Family Pyramidellidse. Elon- 

 gated, many-whorled ; aperture simple, attenuated above, effuse 

 below ; lines of growth (marking the form of the outer lip) 

 sigmoidal ; no umbilicus. 



The characters of these four genera which have been figured 

 together are here given in order to shew in what points they differ, 

 and what analogy and gradation of form subsists between them. 



Taking Trochonema as the most depressed and widely umbilicate 

 form, or with simple and very oblique lines of growth, the next 

 step would appear to be Cyclonema or Holojica, in which the umbili- 

 cus is closed, and the lines of growth a little sigmoid, or at least 

 sinuate, below. Eunema is still more elongate, and the lines of 

 growth decidedly sigmoid ; while it is difficult to say if E. pagoda 

 more properly belongs to this genus or to Loxonema, in which the 

 edge of the outer lip, indicated by the lines of growth, is sigmoid, 

 and the entire form elongated. 



