WHITEAVE8.] ORETACEOtJS FOSSILS, NORTH WEST TERRITORY. 161 



three millimetres near the aperture : umbilicus wide and shallow. 

 Volutions about five in number, increasing rather rapidly in size, but 

 more rapidly in a dorso-ventral than in a lateral direction, not very 

 closely embracing, nearly the whole of the sides of the inner ones being 

 exposed : umbilicus, as measured from suture to suture, occupying 

 about one-third of the entire diameter, and nearly equal in width to the 

 height of the aperture just outside of its emargination. Aperture 

 narrowly subellijjtical, higher than broad, pointed above and very 

 shallowly emarginated below by the slight encroachment of the pre- 

 ceding volution. 



On the outer volution, each of the sides is ornamented by doubly 

 flexuous, transverse and rib-like raised plications, which are inter- 

 rupted by or do not pass over the prominent keel on the periphery, 

 and which are entirely devoid of tubercles. Most of these plications 

 extend completely across the sides, and some of them bifurcate or even 

 trifurcate at about their mid-length, but near the keel a short fold is 

 occasionally intercalated between two of the longer plications. 



The characters of the sutural line are not satisfactorily exhibited in 

 any of the specimens collected. In a small cast of the interior of the 

 shell, whose longest diameter is about three-quarters of an inch, three 

 lobes and as many saddles can, it is true, be counted on one side of the 

 siphonal saddle, but the whole of the exposed surface of this cast is so 

 much worn that nearly all the finer incisions and ramifications of the 

 sutures are obliterated. 



Dimensions of the largest and most perfect specimen obtained; 

 greatest diameter sixty-two millimetres : width of umbilicus, as 

 measured from suture to suture, twenty-three mm. : height of aper- 

 ture, inclusive of keel, twenty-two mm. 



In addition to the specimen whose dimensions have just been given, 

 six much smaller examples, and several impressions or fragments of 

 others, were collected. 



This shell is certainly very closely related to the SchloenbacMa 

 propinqua, from the "Lower Sandstones or Division B" of the Creta- 

 ceous rocks of the Queen Charlotte Islands, and may prove to be only 

 a local variety of that species. .ludging by the rather scanty material 

 at present available for comparison, the present form appears to differ 

 from the typical S. propinqua in having more slender whorls (in a 

 dorso-ventral direction) and a consequently wider umbilicus, — in its 

 more distinctly doubly flexuous folds, and in the greater j)rominence 

 of its abdominal keel. S. borealis seems also to be very nearly allied 

 to the Schloenhachia cultrata (the Ammonites cultratus of d'Orbigny) of 

 the French Neocomian, and to differ therefrom in almost exactly the 

 same way as it does from S. propinqua. 



