BRACHIOPODA. 293 



have the single species S. ampla, Hall ; in the Hamilton group the genus is not 

 represented, but reappears in the early Chemung faunas in S. calata, S. reversa 

 and S. hybrida, Hall, the last two occurring both in New York and Iowa. 



Genus LEPTELLA, gen. nov. 



PLATE SVa, figs. 12-16. 



1862. Leptmna, Billing.s. Pateozoio Fossils, vol. i, pp. 73, 74, tigs. 6t), a, b, G7, a, b, c, p. 219. 



1863. Leptmna, Billings. Geology of Canada, p. 231, figs. 242, 243. 



By the courtesy of Mr. J. F. Whiteaves, an opportunity has been afforded of 

 studying the original specimens of the species described by Mr. Billings as 

 Leptmna sordida, from Limestone No. 2, at Point Levis. These are in a silicified 

 condition and show very clearly all the essential features of their structure. 

 Though they are small, concavo-convex shells with an external aspect like that 

 of LepTtENA or Plectambonites, the character of the interior is such as to pre- 

 clude the admission of the species into any of the generic divisions now recog- 

 nized. A new name is therefore proposed for them. 



Diagnosis. Shells small, normally concavo-convex. Outline semicircular or 

 semielliptical. Hinge-line straight, making the greatest diameter of the shell. 

 Pedicle-valve evenly convex, cardinal area moderately high, delthyrium for 

 most of its extent, covered by a convex plate ; teeth inconspicuous and un- 

 supported by lainelliB ; muscular impressions undetermined. Brachial valve 

 slightly concave ; cardinal area comparatively high ; the delthyrium filled by the 

 cardinal process, which, as viewed from behind, is divided by a median groove 

 for its entire height. On the cardinal margin this process is double but less 

 conspicuous than the crural plates, which are arched, and highly elevated above 

 the hinge-line. They are short, terminate abruptly, and enclose deep sockets. 

 The visceral area is flattened or concave, its anterior margin forming a double 

 curve, from which line the surtace of the valve is abruptly deflected. This 

 visceral area is divided by a broad median ridge and its surface covered with 

 fine, sharp radiating lines which end at the line of deflection. 



Type, Leptana sordida, Billings. Quebec group. 



