20 CANADIAN FOSSILS. 



the Birdseye limestone ; that in the Trenton limestone (pi. 38, fig. 7) 

 seems a more elongate species. Our specimens may however be 

 distinct, as the author does not mention the small carina round the 

 sutural edge of the whorl, conspicuous in M. bicincta when young, 

 but much fainter when full-grown. The base too is less convex and 

 the umbilicus more distinct. But these are minute differences, and 

 from examination of a series, I am much disposed to unite the two 

 species. 



Locality. — Allumette Island. There is another species associated 

 with these, and differing chiefly by having strong upper and lower 

 keels ; and there are several new Plcurotomarice, distinguished by 

 their shortened form from the present genus. 



M. SEREATA, N. Sp. 



Fig. 1. 



M. late conica, spird brcvi ; anfractibus 4 acuficarinatis, carinis 4 serratis T 

 spaliis intermediis concavis et striis conspicuis ; basi convexo, ore rotun- 

 data. 



The spire is less produced than in the preceding, forming an angle 

 of fully 5-5° or 60°, and composed of four acutely carinate whorls, 

 deeply separated at the sutures. The body-whorl is furnished with 

 four keels — the principal one very prominent about the middle of the 

 body-whorl ; one keel above it, near the suture ; another at an equal 

 distance below ; on the convex base there is a fourth, which surrounds 

 at some distance a rather large umbilicus, the sides of which are 

 very convex. The keels are all more or less serrate, the principal 

 one especially so (and not so much undulated as our figure shews) ; 

 and the spaces between them are deeply concave — that between the 

 upper keel and the suture nearly horizontal, but still hollowed out. 

 The lines of growth are sharp and equidistant, decussating the keels 

 to produce the serrate edges, and bending back considerably to the 

 central prominent one, which is so narrow as not to shew a distinct 

 band. 



This beautiful species is more sharply keeled than any other 

 Silurian species known to me, and reminds one of some of the 

 Carboniferous forms. 



Locality . — Allumette Islands. 



