34 Post-Pliocene Deposits of the St. Lawrence, 



very abundant at Beauport, and, as usual with it, is very variable. 

 The cells represented in fig. 16 belong to the most regular and 

 beautiful variety, which occurs in a state of preservation quite 

 equal to recent specimens. //. pertusa is still one of the most 

 abundant forms on the American coast ; and the study of the 

 diverse forms of cells which occur in the same patch, is very 

 instructive in relation to the errors likely to arise from basing 

 specific distinctions in these creatures on minute differences in the 

 forms of the cells. 



The two last species appear to the naked eye on the stones of 

 the drift, as flat, roundish, white patches, somewhat roughened, 

 like shagreen ; and under a lens of low power disclose the forms 

 of their cells. 



Fig. 11. 



7. Lcpralia quadricornuta. N. S. (Fig. 11.)— This is a large 

 species, the cells being about ^th of an inch in length. It is 

 quite distinct from any species known to me. Its description is 

 as follows : — Cells arranged alternately, ovate, ventricose, smooth 

 on the greater part of the surface, but toward the lower end finely 

 marked with radiating and transverse lines, and at the margins 

 roughened with scaly projections; aperture narrowed, flattened 

 at the distal margin, and armed with four hollow spines, those at 

 the angles strongest ; proximal margin deeply sinuated and pro- 

 jecting. 



The specimens occur abundantly in the lowest part of the 

 deposit at Logan's farm, and are arranged in such a manner as to 



