82 WHITEAVES ON FOSSILS FEOM THE 



inuer whorls are not nearly so well preserved as the outer volution, and the asymmetry 

 and separation of all three are best exhibited in the transverse section afforded by the 

 specimen. 



ApSIDOCERAS INSKiNE. (N. 8p.) 



(Plate XVII.) 



This name is proposed for a large fragment, consisting of a cast of the interior of 

 nearly one half of the outer volution, of a huge nautiloid shell from the Hudson River 

 formation at Stony Mountain, Manitoba, wliich evidently belongs to the genus Apsidoceras 

 of Hyatt.' The specimen is nearly a foot in length, as measured in a straight line, or 

 sixteen inches, if the curvature of the abdomen be followed, and the dorso-ventral 

 diameter of the tube of which it is composed is five inches at the larger end. At its 

 anterior extremity a portion of the body chamber is preserved and in the rest of the 

 specimen twenty septa can be counted. 



The whorls appear to have been just in contact, and they were evidently coiled on 

 the same plane : the umbilicus is broad and deep, its breadth in the actual specimen 

 being about five inches : and, although not a vestige of the shell is preserA^d, the 

 surface appears to have been smooth. The periphery or abdominal region is broad and 

 flattened, the lateral angles are tolerably distinct, and the sides, which are convex near 

 these angles, narrow rapidly to the inner edge or dorsum. As far as can be ascertained, 

 in the imperfect and somewhat distorted state of the specimen, the outline of a trans- 

 verse section of the outer whorl at its thickest end, and probably that of its aperture also, 

 would be very broadly subovate, with the larger end of the ovoid truncated, the dorso- 

 ventral and lateral diameters in this region being nearly equal. 



The septa are about twelve millimetres apart in the centre of the periphery or 

 abdominal region, and about five millimetres apart on the narrow dorsum. Each suture 

 has a broad and angular sinus or lobe on the abdomen or venter and a corresponding 

 and similar saddle on both of the outer and lateral angles. On the sides, the sutures are 

 nearly straight or very faintly concave, while those on the dorsum are so imperfectly 

 preserved that it is scarcely possible to trace them throughout their entire course, though 

 each suture in this region seems to have been shallowly curved in such a way as to 

 form a small and feebly deA'eloped saddle on each side, with a similar lobe or sinus in 

 the middle. The angularity of the lobes and saddles on the venter and ventro-lateral 

 angles is most marked near the body chamber. All the lobes and saddles, too, are of the 

 simplest type, their margins being entire throughout. 



The fine specimen upon which the preceding description is based was presented to 

 the Museum of the Survey in the spring of 1889 by the President and members of the 

 Manitoba Historical and Scientific Society. 



A. insigne is more nearly related to the Nautilus Hercules of Billings,- from the Hudson 

 River formation of Anticosti, which is probably an Apsidoceras, than to any other species 

 known to the writer. Still the two forms appear to be totally distinct, for N. Hercules is 



■ Bost. Soc. Nat. Hist. Proc. 1883, xxii. 289. 



'' Described Geol. Surv. Can., Rep. Progr., 1853-56, pp. 306, 307. 



