4G2 Canadian Record of Science. 



No marginal furrows seen. Ocular tubercle close to the 

 hinge line; a narrow diagonal furrow behind the eye 

 extends to the lower end of the anterior marginal curve. 



Sculpture. — Along the lower margin are fine anastomo- 

 sing ridges ; the decorticated part of the valve shows the 

 lower margin of a semi-circular muscle scar, directly 

 behind the ocular tubercle, near the hinge line. Another 

 example of the valve with the surface somewhat corroded 

 shows small pits and also anastomosing ridges on the 

 surface. 



Size. — ^Length, 4:h mm. : width, o\ mm. ; depth of a 

 valve, 1 mm. Another example is 3 J mm. wide. 



Horizon, and Locality.- — ^Assise, E. 1 e. Lower Etche- 

 minian at Dugald Brook. Scarce. 



A form similar to this in size, though proportionately 

 wider, occurs in the same assise ; and another smaller, 

 broader and flatter, is found is found in the assize E. 3 e 

 Upper Etcheminian, at the same brook. 



The following are dimensions of some valves : 

 E. 1 e. left valve, length 4| mm. width, 3| mm., depth, 1mm. 

 E. 1 e. carapace, " 4i mm. " oh mm., " 3^mm. 

 E. 3 e. left valve. " 4| mm. " 3 mm., " 1 mm. 



Xestoleberis, Sars ('65), as represented by Prof. T. 

 Eupert Jones' species S. WrigMii, from the Ordovician of 

 Kildare, Ireland, is like this in form, but is more tumid, 

 and is not shown to possess an ocular tubercle. 



Mutation prima, n. mut. PL II., 9 a to c. 



A form resembling this species, but longer and larger j 

 is found in the gray shale of the volcanic rocks. The 

 example is a complete carapace, and the valves are crushed 

 somewhat and displaced. There appears to be an ocular 

 tubercle near the anterior end, and the fullest part of the 

 valves is in the lower half. 



8cul])ture. — The surface is corroded, Ijut there are traces 



