336 PALEOZOIC PALEONTOLOGY. 
Remarks.—This is a common species of the “trilobite bed” in the 
Nearpass section and is apparently distinct from any of the described 
species of the genus. 
PTEROPODA. 
HYOLITHES CENTENNIALIS Barrett. 
Plate XLIII., Fig. 15. 
1877. Hyolithes centennialis Barrett, Ann. Lyc. Nat. Hist. N. Y., 
Vols XG: 2 2998 
1888. Hyolithes centennialis Hall, Pal. N. Y., vol. V., pt. IL, Supp., 
p. 6, pl. 114, figs. 21-23 (Supp. to Pal. N. Y., vol. VIL.) 
Description—Shell subtrigonal or nearly semi-circular in cross- 
section, tapering gradually backward from the aperture to the ob- 
tusely-rounded posterior extremity, the sides converging a little more 
rapidly towards the posterior end. Ventral side slightly convex, 
lateral edges narrowly rounded, dorsal side strongly convex, more or 
less angular along the median line. Surface covered with fine, some- 
what irregular, crowded, transverse lines of growth. 
The dimensions of a specimen incomplete posteriorly are: length, 
20 mm.; diameter at aperture, 10 mm.; diameter at broken pos- 
terior extremity, 3 mm.; thickness at aperture, 4.5 mm. 
TENTACULITES ACULA Hall.? 
Plate XLIII., Fig. 11. 
1888. Tentaculites acula Hall, Pal. N. Y., vol. V., pt. I1., Supp., 
p. 6, pl. 114, figs. 15-17. (Pal. N. Y., vol. VIL, Supp:) 
Description.—A species of Tentaculites occurs rather commonly in 
the “trilobite bed,’ but the surface of the shell adheres so firmly to 
the matrix in which it is imbedded that in no case have the finer 
surface characters been observed. The internal casts resemble a 
