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. codata, 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. Lept&na, Billings. Palaeozoic Fossils, vol. i, pp. 73, 74, figs. 66, a, b, 67, a, b, c, p. 219. 
1863. Leptcena, 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 
Leptcma 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 LEPTiENA 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 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. 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 surface 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, Leptcena sordida, Billings. Quebec group. 
