GASTROPODA. 261 



on the same plane, concave toward the suture; aperture subangularly ovate, sinuate on 

 the right and left sides, and the shell extended in front. Surface marked by two strong, 

 spiral depressions corresponding to the sinuosities of the aperture, and crossed by 

 lamellose striae which are strongly undulated on the sinuosities of the last volution, and 

 are marked by other undulations on the earlier volutions, indicating former sinuosities 

 in the margin of the aperture." — Hall, 1859. 



Remarks — An incomplete and exfoliated specimen is the only example representing 

 this species. The apex is missing, hence the character of the complete specimen cannot 

 be definitely determined. The distinctly trilobate form, and the clearly defined spiral 

 depressions are the characters used to identify the species. Surface is irregular, lumpy, 

 or nodose in character. Shell surface unknown. 



Horizon — Lower beds. 



Figured specimen No. 27516, Walker Museum. 



Genus Diaphoro stoma Fisher 



Diaphorostoma ventricosum (Conrad) 

 Plate 70, figures 6-8 



1859. Platyostoma ventricosa Hall, Nat. Hist. N. Y. Pal., vol. 3, p. 300, pi. 55, fig. 



9a, b, c; p. 469, pi. 112, figs. 1-10; pi. 113, figs. 7, 8; pi. 115, fig. 8, 1861. 

 1892. Platyostoma ventricosa Conrad, Jour. Acad. Nat. Sci., Phila., vol. 8, p. 275, pi. 



17, fig. 5. 

 1900. Diaphorostoma ventricosum Clarke, Mem. N. Y. State Mus., vol. 3, No. 3, p. 30, 



pi. 3, figs. 25-28. 

 1913. Diaphorostoma ventricosum Ohern, Geol. Surv., Md. Low. Dev., p. 482, pi. 87, 



figs. 1, 2. 

 Description — Shell globose, spire slightly elevated, in a few cases depressed; whorls 

 three, closely coiled, expanding rapidly until the last one or body whorl becomes highly 

 ventricose; volutions flattened on upper side, curving obliquely on the lower, giving the 

 shell a twisted appearance. Aperture subcircular, greatest diameter 40 mm., inner. 

 lip of peristome reflexed. ■ Surface of shell marked by indistinct transverse striae, which 

 parallel the lines of growth. 



^ Remarks — This species is fairly abundant in the collection, both mature and im- 

 mature individuals being present. The flattened upper surface, and the pronounced 

 ventricosity of the body volution characterize all the specimens. Some of the smaller 

 ones may be readily confused with Diaphorostoma depressum Conrad, and the only 

 apparent distinction is the greater tendency to ventricosity in the outer volution. 

 Horizon — Lower and upper beds. 

 Figured specimens No. 27508, Walker Museum. 



Order Opisthobranchia 

 Suborder Pteropoda 



Family Hyolithidae 

 Genus Hyolithes Eichwald 



Hyolithes cf. oxys Clarke 



Plate 69, figure 17 



1908. Hyolithes oxys-Clarke, Mem. N. Y. State Mus., vol. 9, pt. 1, p. 143, pi. 12, figs. 

 10-13. 

 Description — Shell large, conical, sides tapering gradually, length approximately 

 42 mm., diameter of aperture 16 mm. Dorsal face strongly convex; ventral face not 



