CARBONIFEROUS AGE. PERMIAN PERIOD. 65 



Of the large number of older fossU species referred to the genus Nautilus, some 

 undoubtedly belong to distinct genera, while others fall into subgeneric groups, 

 differing more or less from the recent typical forms. If we admit Discites, Trema- 

 todiscm, Gri/ptoceras and several other equally marked forms into this genus, we 

 may regard it as dating back to the Silurian epoch. Species approximating the 

 typical Nautili, however, did not exist, so far as known, before the Carboniferous 

 period, and even the few of modern aspect then introduced, present peculiarities 

 in their septa, or in the position of the siphon, that readily distinguish them from 

 the more recent types ; while the great majority of their supposed congeners of 

 that epoch are stiU more aberrant. The same may also be said in regard to the 

 known Permian species. 



In the Triassic and Jurassic rocks, along wirh some of more modem aspect, we 

 meet with a number of species which, from the lobed or sinuous character of their 

 septa, and other peculiarities, seem to form sections or subgenera, and apparently 

 in some instances, distinct genera. The Cretaceous and Tertiary rocks, as might 

 be expected, contain a larger proportion of true Nautili, but even in the Tertiary, 

 the older type of structure is repeated in the genus Aturia, of Bronn (= Aganides, 

 Montforf?), which, with a ventral siphuncle, has deep lateral lobes ui the septa, 

 similar to those of Goniatites. 



Some five or six recent species of Nautilus have been described by Conchologists. 

 They are found in the Chinese and Indian Seas, Persian Gulf, &c. As they have 

 rarely been seen alive, little is known in regard to their habits, 



IVautilus eccentricuis. 



(Plate II, Pig. 14, a, b.) 

 Nautilus eccentricus, Meek & Hayden, Trans. Albany Inst. IV, 1858. 



Shell small, somewhat compressed ; volutions apparently not more than one and a half, not embracing, rounded 

 excepting near the aperture, where the non-septate portion presents an oval transverse section. Umbilicus wide, 

 shallow, and showing all of each whorl. Septa moderately concave ; siphon small, placed about half way between 

 the centre and the outer, or dorsal side. Aperture transversely oval. (Surface unknown.) 



Length, 0.70 inch ; height, 0.53 inch ;. breadth at the aperture, 0.43 inch ; small diameter of aperture, 0.25 inch. 



"We have some doubts in regard to the propriety of retaining this species in the 

 genus Nautilus, since it seems to consist of little more than one entire whorl, 

 apparently surrounding an open central space. In this character (if it is not due 

 to some accident), as well as in the eccentric position of the siphuncle, it would 

 seem to present affinities to the genus Gyroceras ; from which, however, it differs 

 in having the whorls coiled so as to come in contact. Excepting in the rounded 

 or non-sulcate character of the whorls, it appears to approach the group Tremato 

 discus. 



Locality and position. — Near the mouth of Smoky HiU fork of Kansas River. 

 Permian. (Type 4185.) 



9 June, 1864. 



