260 PROCEEDINGS OF THE ACADEMY OF 



Nautilus (Temnocheilus) Niotensis, M. & W. 



Shell attaining a large size, globose-subdiscoidal ; umbilicus deep, and (con- 

 sidering the lateral margins of the whorls its limits) about twice the dorso- 

 ventral breadth of the outer turn. Volutions about three, contiguous but not 

 embracing, broadly rounded over the dorsal and ventral sides, and promi- 

 nently angular around the middle of each lateral margin ; section trans- 

 versely elliptic, the two extremities of the ellipse being angular. Septa rather 

 distinctly concave, and distant on the outer side less than half the dorso- 

 ventral diameter of the whorls at the point of measurement, making a 

 broad backward curve in crossing the inner and outer sides of the whorls, 

 and curving forward to each of the lateral angles ; siphon piercing the septa 

 less than its own breadth outside of the middle. (Surface and aperture 

 unknown 1 ). 



Greatest diameter, measuring across the disk, about 8*50 inches ; convexity, 

 or transverse diameter of the whorls, 5 inches ; dorso-ventral diameter of the 

 last volution, about 3 inches. 



This species belongs to a group of carboniferous Nautili, including N. coro- 

 natus, McCoy, and N. bianyulatu'', N. multicarinatus and N. cariniferous, Sow- 

 erby, &c. These shells are characterized by having a broad, deep, open 

 umbilicus, showing all the volutions, with the outer side of the whorls broadly 

 rounded or flattened, and the middle of each lateral margin prominently angu- 

 lar ; the angle being sometimes nodose, while the transverse diameter of the 

 volutions is always greater than the dorso-ventral. The siphon in these 

 ehells is generally, 'or perhaps always, between the middle and outer side of 

 the whorls. Although Prof. McCoy included a much wider range of forms in 

 his group Temnocheilus, we think it would be better to restrict it to such 

 species as those mentioned above, all of which were originally included in the 

 group by Prof. McCoy. 



Specifically, our shell is perhaps most nearly allied to Nautilus cariniftrous, 

 of Sowerby, (Min. con. pi. 482, f. 3 and 4) though differing in its proportion- 

 ally wider umbilicus, merely contiguous volutions, and particularly in never 

 having longitudinal ridges on the outer side of the whorls, at any stages of 

 growth. It also differs in having its septa crossing the outer side of the 

 whorls with a broad backward curve, instead of passing nearly straight over. 



Locality and position. Niota and Warsaw, Illinois. Keokuk Division of 

 Subcarboniferous Series. 



Subgenus DISCITES, McCoy, 1844. 



Nautilus (Discites) oknatus, Hall. 



Var. amplds, M. & W. 

 The shell we here place provisionally as a variety of Nautilus (Discites) 

 ornatus, Hall, agrees very nearly in most of its characters with that species, 

 but differs in its much larger size, and the proportionally greater dorso-ven- 

 tral diameter of its volutions, (particularly the outer one), as compared with 

 the breadth of its truncated periphery. In the New York form, these propor- 

 tions, according to the published figure, (Thirteenth Regents Report, 1860, p. 

 102), are about as two and one-third to- one, in-the outer whorl, and nearly 

 equal in the inner turns ; while in our shell they bear the proportions of three 

 to one, the flattened sides of the outer volution being three times as wide as 

 its truncated periphery. The type of the New York species is also described a9 

 having its " siphuucle dorsal." If by this it is meant that the siphon is in 

 contact with the outer side of the shell, as in the Goniatites, then there can 

 be little doubt in regard to the form under consideration being a distinct 

 species, since its siphou is separated from the periphery by a space about 

 equalling its own breadth. It is probably distinct from the New York species, 

 but as individuals of these older types of Nautilida: seem to have varied more 



[Dee. 



