300 PALMONTOLOGY OF NEW YORK. 



There arc; at least three well known species which are clearly referable to 

 this proposed genus : Leptana subquadraia, Hall,* from Perry county, Tennessee, 

 referred to the age of the Lower Helderberg group ; Leptmna tenuicincla, McCoy, 

 elaborately described by Mr. Davidson,! from the Upper Llandeilo and the 

 Caradoc series ; Pledamhonites ovata and P. oblonga, Pander, which are united 

 by UE VerneuilI under the term Leptana oblonga, from the Lower Silurian 

 Ijeds in the vicinity of St. Petersburg. Davidson includes in L. tenuicinda the 

 Lepfana ccnigma of ue Verneuil,§ from the Lower Silurian Ijeds of the Lsland of 

 Gotland, a shell mucli less elongated than the typical L. tenuidnda, and whose 

 interior has not been described. 



Genus LEPTiENISCA, Beeciier. 1890. 



PLATE XV, FIGS. 30, 31; AND PLATE XVA, FIGS, in-30. 



18.59. LepkeiM. Hall. Paleontology of N. Y., vol. iii, p. 197, pi. xviii, iig. 2, 



1S83. Leptwna? (sub-genus?), Hall. Kept. N.Y. StateGeologist for 1882 ; Expl. pi. xv (46), tigs. 30. 31. 



1890. Lf'ptmnisca, Beecher. American Journal of Science, vol. xl, p. 238, pi. ix, tigs. 1-9. 



Diagnosis. " Shell concavo-convex, attached to foreign objects by calcareous 

 cementation of the ventral beak. Valves articulated by the teeth and sockets. 

 Dorsal or socket valve concave ; interior with a broad, more or less defined, 

 spiral impression on each side of the median line, making a single volution. 

 Adductor impressions small. Cardinal line [area] narrow, bearing in the center 

 two prominent, bilobed, cardinal processes, separated to admit the vertical 

 septum in the opposite beak. Ventral valve convex, area elongate-triangular, 

 fissure covered with a pedicle-sheath. Cardinal muscular scar supported on, or 

 limited by a vertical septum, on each side of which, in the anterior half, is a 

 small adductor scar. Shell-structure punctate. 



" Type, Leptana concava, Hall."* Lower Helderberg group. 



This interesting genus includes a few species of attached shells having the 

 general form and contour of Plectambonites, but with a peculiar combination 



*This species is tirst mentioned and illustrated in the Report of the N. Y. State Geologist for 1882, 

 explanation of plate xv (46), tigs. 32, 33. 1883. 



t British Silurian Brachiopoda, pp. 326-328, pi. xlvii, figs. 7-1 S. 



X Geologie de !a Russie, etc., p. 228, pi. xv, fig. 2. 



§ Bulletin de la Soci6t6 Geologique de Fi-ancc, 2e Ser., vol. v, p. 340, pi. iv. fig. 6. 1S48, 



II Bkkcmkh. "On LuiT.'Ti.NLSf'A, a newjgeniis of Bi-.-u-hiiipod from (lie Lower Helderberg group" (op. cit.) 



