THF; FAUNA OF THE 8T. JOHN GEOUP. 57 



third, and is nearly straight in the anterior two thirds of its length ; the apex is broken 

 otF, but projected beyond the line of the ventral side. 



Sculptm-e. This is a thin flattened shell marked by abont scA'en prominent ridges at 

 the dorsal side and about live at the ventral, the difference being due to the intercalation 

 of additional ridges on the dorsal side; some of these ridges are rounded and others have 

 sharp edges ; there are no radiating striœ visible ou the surface when examined with a 

 lens of oue-inch focus. 



Slenotheca pavpera, from the Cambrian limestone of Conception Bay, Newfoundland, has 

 some resemblance to this species, but has not so many concentric ridges. It is not figured 

 by Mr. Billings. 



Length, from the base of the detached apex to the middle of the aperture, 2f mm. 

 Width of aperture, 3 J mm. 



Horizon aud Locality. In the dark grey shales of Div. l.d at Porter's Brook, St. Martin's. 

 Rare. 



StENOTHECA CONCENTRICA, u. sp. (Plate VI. Fig. 11.) 



Outline of the shell lenticular, more strongly arched on the dorsal than on the basal 

 side. Dorsal slope about twice as long as the ventral. Apex depressed, projecting \>\\t 

 little beyond the general outline of the dorsal and ventral slopes. In the shell as com- 

 pressed in the shales, there is a faint rib or internal carina all around the dorsal and ven- 

 tral slopes ; the dorsal third is more rigid than the rest of the shell, and is divided from 

 the lateral slope by a faint sulcus. 



Sculpture. The surface is marked by numerous strong concentric ridges, which are 

 more numerous on the dorsal than on the ventral slope, there being about twelve on the 

 dorsal and eight on the ventral ; the additional ridges are intercalated mostly at the junc- 

 tion of the dorsal and lateral slopes. The surface of the shell is also marked by fine con- 

 centric striœ, invisible to the naked eye, and by very fine radiating striœ scarcely visible 

 with a lens of one-inch focus ; these radiating striœ give the surface of the concentric 

 ridges a minutely cancellate appearance. 



The substance of the shell in this species is thin, and appears to be calcareous, and the 

 flattened sides of the shell are sometimes found displaced, aud one half pushed slightly 

 past the other as if detached along the dorsal and ventral line. 



This species may be compared with Stenotheca cornucopia of the Menevian group, but 

 it differs from that species in its wider aperture and strongly arched dorsal slope. 



Length, from summit of the dorsal curve to the middle of the aperture, 2] mm. Width 

 of aperture, 4h mm. 



Horizon and Locality. In the fine dark shales of l.d, at Porter's Brook, St. Martin's. Not 

 infrequent. 



Stenotheca radiata, u. sp. (Plate YI. Fig. 12.) 



Outline of the shell lenticular, more strongly arched on the basal than on the upper 

 side. Dorsal slope about three times as long as the ventral. Apex more depressed than 

 in the preceding species ; ventral slope concave. As compressed in the shale there are 

 two sulci on the side, viz., one at the dorsal third and another dividing the middle froin 

 the ventral slope. 



Sec'. IV., 1885. S. 



