. College collection of palaeontology. . 108 MOLLUSCA. No. 345. [574, CastJ. Nautilus pseudo-elegans, d'Orb. This tiue specimeu is an inner cast, and shows the septa of the shell. From the Chalk of Rouen, France, and now in the Ward Col- lection, University of Rochester. Size. 6 X 5. No. 246. Nautilus semistriatus, d'Orb. This large specimen is from the Middle Lias, Charmouth, England. No. 247. [595, Cast]. Nautilus Maximus, Conrad. This species is more loosely coiled than any of the preceding. The umbili- cus is wide and deep, and the chamber of habitation is verj' large. From the Hamilton Gr
. College collection of palaeontology. . 108 MOLLUSCA. No. 345. [574, CastJ. Nautilus pseudo-elegans, d'Orb. This tiue specimeu is an inner cast, and shows the septa of the shell. From the Chalk of Rouen, France, and now in the Ward Col- lection, University of Rochester. Size. 6 X 5. No. 246. Nautilus semistriatus, d'Orb. This large specimen is from the Middle Lias, Charmouth, England. No. 247. [595, Cast]. Nautilus Maximus, Conrad. This species is more loosely coiled than any of the preceding. The umbili- cus is wide and deep, and the chamber of habitation is verj' large. From the Hamilton Group (Devonian), of Madison Co., N. Y. Diameter, 14. No. 248. [580, Cast]. Lituites undatus, Conrad. This rare and remarkable shell is a Palfeozoic ally of the jyautilus, from which genus it differs mainly by the complete exposure of all its whorls, and the straight- uess of the last chamber. It appeared in the earliest Silurian. From the Black River Limestone (Lower Silurian), Middleville, N. Y. FAMILY ORTHOCERATIDiE. Tliese tetrabranch ceiilialopods were the ]3riiices of mollnsks in Palaeozoic times, being more abundant and attaining a larger size than any other fossil shell. They resemble in general mi- coiled JVautilidw, being conical shells divided by simple septa, concave next the outlet. The sij^hnncle is usually central, but sometimes marginal, and always complicated. The shell is some- times curved, but never completely coiled as in the JS^atitilus^ and the animal was probably unable to withdraw itself into the shell—the body chamber being relatively smaller than that of the Nautilus. The shell, however, was essentially external. They appear in the Cambrian, culminate in the Silurian and dis- appear in the Triassic. 1200 species have been named. Some authors include them under Nautilid?e. These tetrabranchs were ]3robably the chief agents in perform- ing the duties allotted to the marine carnivora. The New York specimens are most numerous in the Trenton Limestone. Tho
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