GASTROPODA. 255 



1913. Orthonychia tortuosa Ohern, Geol. Surv., Md. Low. Dev., p. 469, pi. 79, figs. 

 10-12. 



Description — Shell erect, elongate, conical, ascending spirally and forming slightly 

 more than one volution; whorls widely separated and expanding regularly to the aper- 

 ture. Inner side of spire distinctly corrugated spirally. Aperture sub-circular, peristome 

 undulated. Surface marked with fine concentric striae, which are closely crowded, 

 wavy and parallel the undulations of the peristome. 



Remarks — This species presents considerable variety in shape, rapidity of expansion 

 of volutions, and in the distinctness of the corrugations. An average individual meas- 

 ures from 45 to 50 mm. from apex to peristome, while larger forms measure as much as 

 65 mm. in height, hence displaying a closer relationship in size to the Gaspe forms than 

 to those of New York. Internal casts only occur, in a few cases with portions of the shell 

 attached. The corrugations apparently are not a persistent feature, in some examples 

 they are strongly marked, in others practically absent. 



Horizon — Lower beds. 



Figured specimen No. 27513, Walker Museum. 



Genus Platyceras Conrad 



Platyceras angular e Rowe 



Plate 68, figures 3, 4 



1913. Platyceras angulare Rowe, Geol. Surv., Md. Low. Dev., p. 476, pi. 85, fig. 3. 



Description — Shell moderately elevated, sub-conical, sides sloping regularly from 

 aperture to apex, one whorl. Apex incurved but free; aperture elongate oval in outline. 

 The shell substance is missing, but the cast shows from 4 to 6 angular, longitudinal 

 ridges occurring at irregular distances from each other, and separated by broad, shallow 

 depressions, and extending from the aperture to very near the apex where they become 

 obsolete. Indistinct elongate nodes mark the ridges. The dimensions are: Length 

 from beak to outer edge of aperture 37 mm., length of aperture 27 mm., width of aper- 

 ture 25 mm. 



Remarks — One specimen, a cast of the interior has been observed. The general 

 depressed appearance, and the sharp angular ridges separated by broad shallow grooves, 

 suggest its affinity with the species described by Rowe. The specimen reveals in addi- 

 tion the character of the -apex, and the general outline of the aperture. 



Horizon — Lower beds. 



Figured specimen No. 27514, Walker Museum. 



Platyceras depressum sp. nov. 

 Plate 69, figures 15, 16 



Description — Shell of medium size, depressed ovoid, consisting of three closely 

 contiguous whorls; spire depressed below plane of body volution whose upper side is 

 inclined toward the depressed spire. Lateral surface sloping obliquely downward, 

 slightly concave, giving rise to a ridge-like lateral border. Whorls gradually expanding 

 from apex to aperture, the aperture not well shown, but apparently vertical, and from 

 triangular to sub-quadrilateral in outline. Suture lines deeply impressed. 



Basal view showing a wide, deep umbilicus. Surface characters obscure; a small 

 portion of shell adhering near the umbilicus exhibits indistinct transverse striae which 

 have a tendency to sinuosity. Exterior surface rough, but not nodose as in Platyceras 

 nodosum Conrad. Surface of the cast generally rough, possibly indicating a rough or 

 somewhat nodose shell surface. 



Remarks — There are present in the collection two entire casts and a fragmentary 

 portion of a third. This species is distinguished from all the other Platycerids present 



