184 



front half of the space thus enclosed is a faint outline of a visceral callus 

 of a lozenge shape. The position of the vascular trunks is probably out- 

 side of the horns of the crescent, thence extending forward ; about a third 

 or a quarter from the front of the shell is a crescentic row of short vas- 

 cular grooves. In front of this row of grooves are one or two growth 

 ridges, and the flattened border of the valve. 



The dorsal valve is orbicular in outline ; its height is less than half of 

 that of the ventral. The valve is strongly arched in the posterior half, 

 but somewhat flattened on the posterior lateral slopes. Interior. This 

 is marked by three strong radiating ridges in the posterior half of the 

 valve ; at the origin of these ridges are a pair of pits with a small tubercle 

 in each, marking the position of the cardinal muscles. Of the three 

 radiating ridges, the central is a narrow median ridge, with three sharp 

 keels ; for half of the length of the valve this ridge is prominent, but 

 fades away in the anterior third of the valve ; at the end of this ridge 

 would be the scars of the anterior laterals ( " j." ). The lateral ridges 

 are broader than the mesian one, but not so long ; outside of them are 

 the impressions of the lateral muscles. 



Sculpture. The roughness of the matrix prevent a good presentation 

 of the surface characters of this species. Some examples of the ventral 

 valve show fine concentric ridges, of which there are about ten in half 

 the length of the anterior slope (i. e. about 10 to 1 mm.) ; the surface of 

 these ridges appears to be granular. 



Size. The largest dorsal observed was 3 mm. across, but the greater 

 number are not more than 2 mm. The full-grown ventral is about 2 mm. 

 high, and the dorsal less than one. 



Horizon and locality. In gray flags of Div. 2c on the eastern slope of 

 the valley of McNeil brook, on the road to Trout brook. Found in 

 various attitudes in the sandy bed. The ventrals are both upright, 

 inclined, and lying on their sides in the layers. From this locality Mr. 

 Fletcher has reported Obolella, a genus in which, at the time his report 

 was written, many of these small brachiopods of the Canadian Cambrian 

 were included. 



Comparison Linnarsson described very fully a species like this from the Paradoxides 

 . beds of Sweden.* He found it: to range through the whole of the Para- 

 doxides zone. Our form belongs somewhat higher up. 



From A. Baileyi of the (lower) Paradoxides beds in New Brunswick! 

 this species is distinguished by its smaller size, and as to its interior by 



* Loo. cit. 



t Trans. Roy. Soc. Can., Vol. iii, sec. iv, p. 36, pi. v, figs. 13, 13a, 6 and c. 



