PALEONTOLOGY. 425 



tapering in the upper than in the lower part. Volutions six or six and a half, mod- 

 erately convex on the outer surface, and more strongly rounded on the lower part 

 of the exposed portion than on the upper; suture-line distinct, but not margined 

 by a flattening of the upper edge of the succeeding volution. Aperture elongate, 

 slightly angular at the base, and pointed above. Surface of the volutions marked 

 by a large number of distinct vertical striae, which are more numerous and slightly 

 finer on the body volution than above, and are so nearly destitute of sigmoid curva- 

 ture as to appear vertical until closely examined. 



The small size of the shell, the nearly vertical lines, and the un- 

 equally expanding volutions, are distinguishing features; the latter char- 

 acter, however, appears to vary a little in degree on some of the speci- 

 mens. It will be readily distinguished from the young shells of L. 

 Hamiltonia:, which occurs in the same rock, by the number of volutions 

 and the slender form. 



Formation and Locality. — In the white cherty layers of the Upper 

 Helderberg limestone, near Dublin. Ohio. 



CEPHALOPODA. 



Genus ORTHOCERAS Breyn. 



Orthoceras nunlium. 



Plate III, figs. 1 and 2. 

 Orthoceras nuntium Hall, loth Rept. State Cab., p. 79. pi. 8, figs. 3 and 4. Pal. N. 

 Y., I lust. Dev. Foss., p. 43, figs. 4 and 15. 



Comp. O. subulatum Hall, G?ol. Rept. 4th Dist. N. Y., p. 180, fig., and Pal. N. Y. 

 Illust. Dev. Foss., pi. 38; also O. Thoas and O. Hyas Hall of same work. 



Shell attaining considerable size, the specimen used for description and figured 

 having a length of nine inches, and still imperfect at both extremities, retains only 

 about an inch of the outer chamber, and has a diameter of half an inch at the lower 

 extremity. Section circular; tube moderately increasing in diameter with increased 

 length, slightly curved throughout, and marked by regular encircling annulations, 

 which are elevated, round on the crest, separated by deeply concave interspaces, 

 which regularly increase in distance and also in strength from below upwards. 

 Those of the lower part where the shell is uncompressed and is half an inch in 

 diameter, are about one-tenth of an inch distant from each other; and at the upper 

 end where the diameter is about one and three-fourths of an inch are about three- 

 eighths of an inch from crest to crest. Surface of the shell marked by fine, closely 

 'arranged and sharply elevated concentric striae, and also by longitudinal striae of 

 similar character, but more or less alternating in strength, the two sets giving a 

 finely cancellated structure just discernable to the unassisted eye. Septa very 

 deeply concave and regularly curved, uniting with the shell a little above the crest 

 of each annulation. Siphuncle small and centrally situated. 



The species is of the ordinary annulated type differing from other 

 species of the group only in the strength and comparative distance of 

 the annulations; in the rate of increase in diameter, and in the nature 

 of the surface markings. The shell, like many of the annulated forms 

 of any considerable size from the upper Helderberg and Hamilton groups, 

 shows a slight curvature of the tube, a little more perceptible in the 

 lower part than above. The Ohio specimens correspond more nearly to 



