CEPHALOPODA. 785 
Orthoceras perroti.] 
lations separated by furrows of equal width; sutures regular and lying in the 
horizontal furrows, septa deeply concave and regular, and surface markings consisting 
of fine, closely-set longitudinal lines slightly alternating in size. 
These are characters agreeing with the early descriptions cited, and serve to 
distinguish the species from Orthoceras bilineatum, in which the shell expands more 
rapidly and the concentric striz, which are here obscured or absent, are conspicuously 
developed. 
Formation and locality.—In the Trenton shales at Minneapolis, Minnesota; also at McGregor, Iowa. 
Museum Register, No. 8290. 
ORTHOCERAS PERROTI, Sp. nov. 
PLATE LIY, FIGS. 4 and 5. 
Shell moderately large, very gradually expanding. Cross-section broadly 
subelliptical, nearly circular. Surface covered by closely-set annulations about 
2mm. in width, separated by somewhat narrower transverse furrows. Sixteen of 
these annulations, of equal size and at regular interspaces, occur in a length of 
41mm. These ridges and furrows are crossed by a double series of vertical elevated 
lines alternating in size, upon the summits of the annulations being very conspicuous 
and developed into lamellar expansions. This character (one secondary lamella 
between each two primary lamelle) is maintained over the entire surface, apparently 
without the intercalation of other series. Where best preserved, the surface affords 
no evidence of concentric lines. Sutures regular and transverse; septa evenly 
concave, moderately deep; sipho small and central. 
The specimen showing the above characters is a well-preserved silicified 
fragment retaining the exterior with unusual delicacy. Its length is 50 mm., its 
greatest width 30 mm., and its minor axis at the same plane 26 mm. The species is 
allied to Orthoceras olorus Hall, but its distinguishing features will be found in the 
closer annulations and the different composition of the ornament. 
Formation and locality.—In the Hudson River group at Granger, Minnesota. 
ORTHOCERAS LESUEURI, Sp. nov. 
PLATE LIII, FIG. 4; PLATE LV, FIGS. 8 and 9. 
Shell rather small, slender; subelliptical in cross-section. Surface covered with 
numerous fine, nearly transverse or very slightly oblique annulations, which are 
narrow at the base, abruptly elevated, sloping equally above and below, and separa- 
ted by grooves somewhat broader than the annulations themselves. The latter 
make a very slight backward curve on the dorsal and ventral surfaces, with a broad 
-50 
