Plat. 672 



Platyceras membranaceum, Ringueberg, Bull. Buffalo 



S. N. S., Vol. 5, 1886. Niagnra, VI. 

 Platyceras mitelliforme, new species^ Simpson Trans. 



Amer. Phil. Soc. Philada. 1889, 

 page 456, fig. 26, 1, side view, 

 fig. 2, dorsal view. Shell small, 

 obliquely arcuate from the 

 base; apex incurved, making 

 A.p.s. Tr.i889. --^-^:l_j».j^ p^j.^ of one volution; below 



which the body volution rapidly increases in size. Width at 

 the base equal to three-fourths the length of the anterior side; 

 length of the posterior side less than one-half of the anterior ; 

 right and left sides equally developed. Anterior side convex, 

 with a prominent, broad, rounded carina along the middle ; on 

 each side of the carina, towards the base, a shallow depression. 

 On some of the specimens there are indications of very slight 

 plications on the posterior side. Aperture oblique, broadly 

 elliptical; peristome a little sinuous at the carina, and some- 

 times slightly sinuous, corresponding with the faint folds of the 

 posterior side. Surface marked by concentric lines and by 

 broad undulations, which sometimes give to portions of the 

 shell a lobed appearance. A specimen of about the average 

 size measures as follows ; Height 12 mm. ; length of the ante- 

 rior side 25 mm. ; of the posterior 8 mm. ; width at base 22 

 mm.; thickness 18 mm. The characteristic feature of this 

 species is the prominent carina or elevation along the dorsum. 

 It may be distinguished from Platyceras inequale of this for- 

 mation by its somewhat larger size, the prominent carina, and 

 the equal development of the right and left side; from Platy- 

 ceras dor sale by its smaller size, its flattened form (a trans- 

 verse section being oval), and by the partial volution of the 

 apex ; from Platyceras ( Orthonychia) striatum by its arcuate 

 form, the prominent carina and the absence of conspicuous 

 plications; from Platyceras carinatum by the equal develop 

 \nent of the right and left sides, and the absence of conspicuous 

 plication; from other species at present known, by its small 

 size, decidedly curved form, and prominent carina. — In Penn- 

 sylvania near Warren, in Chemung upper heds. VIII g. 



Platyceras multisinuatum, Hall, Pal. N. Y., Vol. 3,1859. 

 lower Held, VI 



