264 PROCEEDINGS OF THE ACADEMY OF 



P. bivalve, of White k Whitfield, from the Kinderhook group ; but it may be 

 readily distinguished by its much more rapidly expanding whorls and conse- 

 quently larger aperture. It also differs in having the apex of its spire distinctly 

 sunken below the upper side of the body whorl, instead of nearly even 

 with it. 



Amongst foreign species, ours is perhaps most nearly allied to Pileopsis 

 angustata, of Phillips (Geol. Yorks. 11, pi. xiv, fig. 20), from which it also 

 differs in having its whorls much more rapidly expanding, and its aperture 

 proportionally much larger and more rounded. 



Locality and position, St. Genevieve county, Missouri, and Randolph 

 County, Illinois ; from the Chester division of the Subcarboniferous series. 



Platyceras haliotoides, M. & W. 



Shell rather small, ovate, very oblique and depressed ; composed of two very 

 rapidly expanding, nearly or quite contiguous volutions, the last one of which 

 is depressed above, narrowly rounded around the dorsal side, and forms nearly 

 the entire bulk of the shell ; apex of spire on a plane with upper side of the 

 bdy whorl ; aperture large, transversely oval, being wider than high ; lip 

 sometimes sinuous on the outer or dorsal side ; surface with moderately dis- 

 tinct lines of growth. Exfoliated surfaces sometimes showing apparently 

 traces of revolving stria?. 



Length, - 73 inch ; breadth, 0-54 inch ; height, 41 inch. 



This species will be recognized by its very oblique depressed form, and the 

 narrowly round character of the outer side of its holy whorl, which peculiari- 

 ties give it much the form of a Huliotis. Its first turn, which is quite small, 

 seems to have been sometimes free or slightly detatched from the body of the 

 shefl, and in other examples in contact with it. The marks of growth generally 

 indicate a rather broad, moderately deep sinuosity of the lip on the dorsal or 

 outer side. 



Locality and position. Waverly sandstone, fifty feet below the Millstone 

 grit, Richfield, Summit county, Ohio. 



Platyceras pncum, M. & W. 



Shell rather under medium size, in adult examples elongate conical and 

 oblique ; body portion nearly straight, especially on the posterior side ; apex 

 attenuate, pointed, laterally compressed and curved backwards (without any 

 lateral obliquity), so as to form a free hook of ab mt half a turn. Aperture 

 generally a little wider transversely than the antero-posterior diameter, and 

 usually shoeing a faintly subtrigonal outline, produced by the prominence of 

 the front, and the flattening of the posterior side of the body. Lip irregularly 

 undulated, prominent on each side, broadly sinuous behind and provided 

 with a very deep narrow sinus in front. Surface with the usual undulating 

 concentric striae crossed on the lower half of the body by small, rather obscure 

 longitudinal plications, and in front by a larger, but narrow prominent ridge, 

 upon which the lines of growth make a strong upward curve, so as to indicate 

 the presence of the anterior sinus during most of the growth of the shell. 



Length, 1 inch; breadth (transverse diameter of the aperture), - 70 inch; 

 antero-posterior diameter of the aperture, 0"55 inch. 



This species is intermediate in size and some other respects between 

 Plat/jceras acutirostris= ( Capulus acutirostris, Hall) , and Platyct ras equilatera, 

 Hall. In size and general appearance it is most like the former, though it is 

 larger and differs in having its apex merely hooked instead of subspiral, as 

 well as in its prominent anterior ridge and deeper and narrower anterior sinus. 

 From P. equilatera it is distinguished by its smaller size, narrower and straighter 

 form (particularly at maturity), less incurved beak, prominent anterior ridge, 

 deep anterior sinus and portionady smaller aperture. It also wants the 

 antero-lateral sinuses of the lip seen in the typical forms of that shell. 



[July, 



