34 BULLETIN OF THE 



15. Hyolithes Billingsi, Walcott? 



Plate II. Fig. 20. 



Shell small. The dorsal side flattened; the lateral edges distinct, but nar- 

 rowly rounded. The ventral side moderately convex or composed of two 

 flattened surfaces meeting along a rounded median line. Shells are often tri- 

 angular in cross section and are then distinguished from Hyolithes Araericanus 

 by the rounded character of the median line on the ventral side, and their 

 smaller size. In the specimens figured by Walcott, the dorsal side is slightly 

 curved, this concavity being almost filled up again by a low, broad, median 

 elevation. This feature has not been detected in the North Attleborough 

 specimens. The identification of this form is entirely unsatisfactory, owing 

 chiefly to the imperfect material at command. 



Locality and position. — Station No. 1, North Attleborough, Mass., Cam- 

 brian, 6 or 7 specimens. Also at St. Simon and Bic Harbor, Canada, and 

 Silver Peak, Nevada. 



16. Hyolithellus micans, Billings. 



Plate II. Fig. 23. 



Shell very slender, often 22 mm. long, tapering gradually to a pointed ex- 

 tremity. Cross-sections are circidar, unless disturbed by pressure. The surface 

 is marked by fine transverse striae. These strise may be either of approximately 

 equal size or at more or less regular intervals may have intercalated single 

 striae of larger size. The apical angle is 4° or 5°. 



The identification here made is based chiefly upon the slender form and cir- 

 cular outline of the shell. The operculum has not been found. 



Locality and position. Station No. 1, North Attleborough, Mass., Cam- 

 brian, 400 or 500 specimens. Also at Bic and St. Simon, Canada, and 

 Troy, N. Y. 



17. Salterella curvatus, sp. n. 



Plate II. Fig. 22. 



Shell short, curved, rather rapidly tapering. Cross-sections circular. The 

 curvature of the shell can usually be referred to one plane, but sometimes it is 

 slightly irregular, ha\dng what might be called an incipient spiral structure ; 

 the apical angle varies from 8° to 12°. The surface is smooth, or ornamented 

 hy faint, scarcely vi.-;ible transverse striae, in no manner comparable with the 

 much stronger striae of S. pulchella, Billings. 



Locality and position. — Station No. 1, North Attleborough, Mass., Cam- 

 brian, 20 specimens. Also at L'Anse au Loup, Labrador, and Point Levis, 

 Canada. 



