120 



to the body whorl : canal short. Whorls five and a-half or six, convex, 

 angular, those of the spire obliquely compressed above and encircled below 

 the middle by a narrow, very prominent, subnodose, laminar keel, beneath 

 which they are nearly perpendicular, but slope a little inwards ; sutures 

 indistinct. Body whorl also obliquely flattened above, angular and 

 keeled veiy conspicuously above the middle, ventricose, and bearing two 

 minute keels or spiral ridges below, and finally contracting rapidly but 

 unequally on either side into the short canal at the base. Aperture 

 ovately subpyriform, broadly channelled in front; outer lip apparently 

 thin and simple ; pillar devoid of plaits, as far as can be ascertained ; no 

 callus on the columellar side. 



The principal keel,, which encircles the whole shell in a continuous 

 spiral, is raised to a height of nearly, or quite, two lines above the highest 

 general level of the whorls, and is subnodose, or undulated on its edge, 

 in consequence of its being interrupted and crossed by slightly elevated 

 transverse folds and corresponding shallow depressions, at irregular but 

 for the most part rather distant intervals. In addition to this, the entire 

 surface is covered by a fine and delicate network, composed of close-set 

 minute, spiral raised lines, and of densely crowded, transverse, but some- 

 what flexuous etriations. 



Estimated length when perfect, about three inches and four lines ; 

 maximum width, one inch and not quite eleven lines. 



Middle Shales, Division D, of the north-west side of Hornby Island ; 

 J. Richardson, 1872, A single specimen with the apex of the spire and 

 tip of the canal broken off, but with a considerable portion of the test 

 remaining, the sculpture of which is exquisitely preserved. 



' On pages 375-377 of his *' Report on the Invertebrate Cretaceous and 

 Tertiary Fossils of the Upper Missouri Country," plate 32, figure 7<2, 

 Mr. Meek has described and figured a Serrifusus from Dakota, which he 

 proviaonally regards as a varietal form of S. Dakotemis, but which he 

 thinks may belong to a distinct, though closely allied species, for which 

 he suggests the name S. goniophorus. Judging by the solitary specimen 

 collected by Mr. Richardson, the differences between it and the Dakota 

 shell do not appear to the writer to be sufiicient to warrant their being 

 regarded as two distinct species, but the Hornby Island Serrifusus is 

 probably entitled to rank as a well marked variety, characterised 

 principally by the much greater prominence of its revolving, spiral 

 keel. 



