NATURAL SCIENCES OF PHILADELPHIA. 259 



Its last three septa are crowded within a space only equalling one of the 

 uhambers below. 



Locality and position. Charleston, Indiana. Devonian. 



Genus NAUTILUS, Linnaeus, 1758. 

 Subgenus ENDOLOBUS, M. & W. 



Nautilus (Endolobus) teramplus, M. &. W. 



Shell attaining a very large size, compressed subglobose ; umbilicus rather 

 deep, about as wide as the dorso-ventral diameter of the outer volution, and 

 showing about three-fourths of each inner turn. Whorls three to three and* 

 a half, increasing rather rapidly in size, broadly rounded. over the dorsal or 

 outer side, and more narrowly round on each lateral margin, where tlie 

 greatest prominence is a little within the middle ; lateral margins each pro- 

 vided with a row of large, broad, depressed, orsubuodose prominences, about 

 fourteen of which may be counted on each side of the last turn ; from these 

 rows of nodes or mammillary protuberances, the inner side of each whorl 

 rounds abruptly into the umbilicus, and is provided along the middle with a 

 moderately deep, rounded concavity for the reception of each succeeding inner 

 turn. Septa deeply concave on the side facing the aperture ; separated by 

 intervals, measuring, on the dorsal side, more than one third the dorso-ven- 

 tral diameter of the whorls at the point of measurement, passing nearly 

 straight over the broad periphery, and with a very slight forward curve across 

 the sides ; while on the inner concave side they are each deflected abruptly 

 backwards, so as to form a deep, more or less funnel-shaped ventral lobe. Si- 

 phon placed rather more than its own breadth nearer the inner than outer 

 side. Surface of cast smooth. 



Greatest diameter, 20 inches ; transverse diameter, 12 inches ; dorso-ven- 

 tral diameter of inner whorl, 8 inches; breadth of umbilicus, 8 50 inches ; 

 circumference around the periphery, 4 feet 8 inches. 



We know of no shell with which this fine species is liable to be confounded, 

 though it has mu'li the form and general appearance of our N. spectabilis, 

 from the same position. It differs, however, in the position of the lobe on 

 the inner side of septa ; and in having its siphon located farther in from the 

 outer side. In a side view it presents some general resemblance to N. 

 tubcrcufatus, of Sowerby, as figured by Phillip, in his Geol. Yorkshirei i. 

 pi. 22, fig. 29, though even as thus seen, it will be observed to differ in its 

 broader whorls, and in having the most prominent part of their sides, with 

 their nodes, placed nearer the umbilicus, while in a profile view, it will be 

 distinguished at a glance by its periphery being rounded, instead of nearly flat. 



As may be seen by the foregoing description, this species differs from tjie 

 typical Nautili, in the. possession of a peculiar funnel-shaped ventral lobe, 

 formed by the backward flexure of the septa. Hence it seems to bear almost 

 exactly the relations to Nautilus that the genus Tretoceras does to Orthoceras ; ' 

 hence we regard it as the type of a group for which we propose the name 

 Endolobus. 



If Montfort's name, Bisiphites, is to be retained, the name of this shell 

 should doubtless be Bisiphites peramplus, as the type upon which he pro- 

 posed to found a genus under that name, seems to have had an inner lobe 

 which he mistook for a second siphon. As his name, however, implies a plain 

 contradiction of fact, we think it should not be used. 



Judging from Montfort's figure, his type not only differs from ours, in having 

 the outer whorl enveloping all the others, so as to leave no open umbilicus, 

 but in having the lobe of the septa a little removed from the inner side, in- 

 stead of being directly in contact with it, as in our shell. He says his type 

 was a large fossil species, attaining a diameter of two feet. 



Locality and position. Randolph County, Illinois. Chester division of 

 Subcarboniferous Series. 



1865.] 



