Resembling 

 species. 



210 



This shell is referred provisionally to Obolella Belli, Dav., of the Lower 

 Tremadoc in North Wales, which is about the horizon of our species. 

 Davidson remarked that thn " internal characters agree pretty closely 

 with those of 0. sagittalis." On comparing Davidson's figures of the 

 ventral valves of 0. Belli and 0. sagittalis, one may remark differences 

 similar to those which distinguish 0. (L.) misera, Bill, from 0. (L) trans- 

 versa, Hartt, of the St. John Group. Tn 0. Belli and 0. misera the muscle 

 scars are fainter and nearer the back of the shell, and the umbonal callus 

 is smaller than in the other two. 



This species is not common at McLeod brQok. The V-shaped ridge 

 of the ventral valve runs about half way to the front, and is more U- 

 shaped than with the other species. 



The ventral valve has a strongly marked median ridge in the middle 

 third of the length of the valve, in front of this the ridge extends as a 

 low elevation nearly to the front margin. Opposite the high part of the 

 ridge, in the posterior third of the valve, are two strong triangular pits 

 which appear to be muscle scars. The posterior lateral margins of the 

 valve are flattened. 



Sculpture. Often the surface is finely granular, and the dorsal shows 

 a few concentric ridges of growth. 



Size, as stated above. 



Horizon and locality. Fine dark grey shales of Div. (C. 3c,) at Mc- 

 Leod brook, Boisdale, Cape Breton. 



N.B. Mr. Walcott, who has examined the examples from Navy island 

 says they are not L. Belti, Dav, 



Monobolina 

 refulgens. 



MONOBOLINA, Salter, 1865. 

 MONOBOLINA REFULGENS. 



PI. XVI. figs. 2a-b, alsu PI. XI. figs. 4a and b. 

 Obolus refulyens, Matt. Trans. Roy. Soc. Can. vol. ix sec. iv page 44, pi. xii, figs. 6a-d. 



Since the description of this species was written, in 1890, no observa- 

 tions had been made which would define more accurately the internal 

 characters of this shell, or throw additional light on its affinities. The 

 more perfectly preserved shells collected lately in Cape Breton, however, 

 have changed the writer's view of the relation of this species. 



A sharply preserved mould of the dorsal valve shows that the species 

 is congeneric with Obolella (Monobolina) plumbea of the Welsh Lower 

 Ordovician, characterized by the close approximation of the central 



