BRACHIOPODA. 203 



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

 represented, but reappears in the eai-ly 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 XVa, figs. 12-16. 



1862. Leptwna, Billings. Pateozoic Fossils, vol. i, pp. 73, 74, tigs. Gtj, a. h, 67, a. h, c, p. 219. 



1863. Leptmia, Billings. Geolog-y of Canada, p. 231, fig-s. 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 

 Lept&na 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 Lept.ena 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-conve.x. 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 b}^ lamellae ; 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. Tliey 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 witli 

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



Type, Lept(zna sordida, Billings. Quebec group. 



