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 Americanus 
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 circular, unless disturbed by pressure. The surface 
is marked by fine transverse strie. These striae may be either of approximately 
equal size or at more or less regular intervals may have intercalated single 
striz 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 
roy, 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, having what might be called an incipient spiral structure ; 
the apical angle varies from 8° to 12°. The surface is smooth, or ornamented 
by faint, scarcely visible transverse strie, in no manner comparable with the 
much stronger strie 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. 
