Silurian Fossils of Nova Scotia, 147 



rounded or scarcely subangular, about five or six depressed in the 

 flattened sinus of tlie ventral valve and a corresponding number 

 raised on the flattened mesial elevation, which rises abruptly 

 though usually but slightly above the lateral portions of the 

 shell. From ten to fourteen plications mark the surface on each 

 side of the mesial fold and sinus. Plications in front marked by a 

 sharp groove along the centre, and those of each valve deeply 

 interlocking. 



This species resembles the i?. nucleolata of the Lower Helder- 

 berg rocks of New York, and in some specimens it approaches to 

 H.ventricosa, but is always much more finely plicated than either. 

 It closely resembles the E. Wilsoni of Europe in its general form, 

 but the plications are more rounded and somewhat coarser, and 

 while in that species the sinus causes no depression in the ventral 

 valve below the general surface of the shell, in ours there is an 

 abrupt depression as well as a slightly abrupt elevation on the 

 dorsal valve, while there is no similar feature in the R. Wilsoni* 



The Nova Scotia specimens are in all respects identical with 

 those from Tennessee. 



The geological position of the specimen from Tennessee is in 

 rocks of the age of the Lower Helderberg group, associated with 

 Pentamerits galeaius, P. Verneuili, Spirifer macropleura^ Spiri- 

 fer perlamellosay Spirifer cyclopteray and others. 



10. Leptocelia intermedia. Fig. 5, N. sp. 



Shell concavo-convex ; outline semi-elliptical, cardinal extremi- 

 ties rounded, and the hinge-line a little shorter than the greatest 

 width of the shell ; ventral valve moderately convex, carinate in 

 the middle by a strong plication, with six or seven smaller ones 

 on each side, the lateral ones slightly curved towards the outer 

 extremity. Dorsal valve concave, with a broad shallow mesial 

 sinus, the margins on either side being bent a little upward, giving 

 a sinuous outline to the margin of the shell ; surface marked by 

 fine concentric striae. 



This species resembles the L. hemispherica of the Clinton group 

 in New York, in general form, but the hingeyine is shorter and 

 the extremities rounded ; the mesial elevation consists of a single 

 strong plication, while in L. hemispherica the surface is regularly 

 plicated, with the central one sometimes a little stronger than 

 the others. 



♦Sowerby, M. C, vol. ii., page 38, says : The " sinus at the front, al- 

 though deep, does not alter the evenness of the surface." 



