FOSSILS. 595 



adjacent rays are in contact "witli each other outside of the oral plates, 

 and not completely separated as they are in P. Niagarensis. There 

 ai'e six or seven adambulacral plates on each side of the ambulacra! 

 groove in each ray, and they gradually decrease in size from the 

 oral plate outwards to the point of the ray. The width of the 

 ambulacral groove is equal to one-third the width of Fig. 197. 

 the ray, and consequently the adambulacral rows of plates SrvSlxuiii!!. 

 are also each equal to one-third the whole width of the 

 ray. In each groove there are two rows of small and 

 apparently nearly square ambulacral plates, twelve or 

 fourteen in each row, and they seem to be continued 

 round on the inner margin of the oral plates ; the mouth is about 

 one line wide. 



This species differs from P. Niagarensis^ Hall (Pal. N. Y., Vol. 2, 

 page 247, PI. 51, Figs. 21, 22, 23), in being smaller, the rays not so 

 slender, and more importantly in the junction of the adambulacral 

 plates outside of the oral plates. 



The specimen was collected at Arisaig by Rev. Dr Iloneyman, 



2. Mollusca. 



Crania Acadiensis, Hall (Fig. 198). Circular or broadly sub- 

 oval, moderately convex, the greatest convexity near the apex ; apex 

 obtuse. 



Several casts show a central elevated area, with strong muscular 

 impressions ; the more elevated portion being surrounded by a flat- 

 tened border, which is radiatingly striate. 



These specimens are casts which appear to be of the ventral valve ; 

 and the form of the muscular impressions is so characteristic of the 

 genus that I can have little hesitation in thus I'eferring them. Arisaig, 

 East River, coll. J. W. D.* 



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. Arisaig, coll. J. W. D. 

 Three other species of Discina are mentioned by Dr Honeyman as in 

 his Arisaig collections. 



Chonetes Nova Scotica, Hall (Fig. 199). Shell semi-elliptical, 

 width varying from once and a half to nearly twice the length. The 



* Of tlie species from Arisaig thus marked, some sj)ecimeiis were collected by Dr 

 Honeyman, and were placed with my own collections in the hands of Professor lliUl. 



