144 



Silurian Fossils of Nova Scotia, 



ARTICLE XII. — Descriptions of New Species of Fossils from 

 the Silurian Rocks of Nova Scotia. By James Hall. 



1. Crania acadiensis. N. sp. Fig. 1. 



Circular or broadly sub-oval, moderately convex, the greatest 

 convexity near the apex ; apex obtuse. 



Several casts show a central elevated area, with strong muscu- 

 lar impressions ; the more elevated portion being surrounded by 

 a flattened border, which is radiatingly striate. 



These specimens are casts which appear to be of the ventral 

 valve; and the form of the nmscular impressions is so character- 

 istic of the genus that I can have little hesitation in thus referring 



them. 



2. DisciNA tenuilamellata. Var. suhplana. 



Shell broadly elliptical, or suborbicular, externally depressed, 

 apex subcentral ; surface marked by thin sharply elevated lamellae. 



This closely resembles the Niagara species of New York, but 

 may be distinct. Should further examination prove it a distinct 

 species, the name D. suhplana may be adopted. 



Fig. 2. 



Fig. 3. 



Fig. 1. 



Fig. 5. 



Fig. 4. 



3. Chonetes Nova-Scotica. N. sp. Fig. 2. 



Shell semielliptical, width varying from once and a half to 

 nearly twice the length. The ventral valve variably convex, and 

 often showing a flattened or slightly concave space down the 

 middle of the shell ; cardinal margin ornamented by four or five 

 minute spines on each side of the beak ; cardino-lateral margins 

 often a little wrinkled ; surface finely striated, strise flexuous, 

 dichotomising and increasing by interstitial addition, so that 

 there are more than one hundred on the margin of the shell ; 

 strise increasing in size below the umbo ; concentric strise fine, 

 close, rounded and slightly undulating. 



Dorsal valve moderately concave ; strise much stronger below 

 the middle of the shell and sometimes bifurcating toward the 

 margin. 



