347 



due to the abrupt truncation of the ribs there. It is doubtful whether 

 this specimen should be regarded as a well marked variety of P. Haradm, 

 or as the type of a distinct and previously U! described species. 



Pachydiscus binodatus. (N. Sp.) 



Plate 49, figs. 1, & 1«. 

 Shell strongly libbed and moderately inflated, but depressed in the 

 middle on both sides, the umbilicus occupying a little more than one third 



of the entire diameter, though its 

 margin is rounded and indistinctly 

 defined. Volutions rather closely 

 involute, more than one half of the 

 inner ones being covered by those 

 which succeed them, increasing 

 rapidly in size, the outer one round- 

 ed between the ribs and near the 

 aperture, but subpentagonal upon 

 the ribs, where the siphonal region 

 is broadly flattened, and the sides 

 slightly and somewhat obliquely 

 compressed. Between the ribs, and 

 near the aperture, the outline of a 

 transverse section of the outer 

 volution is not far from circular, 

 but wider than high, and concavely 

 and rather deeply emarginate by the encroachment of the preceding 

 volution ; but if taken at the ribs the section is more nearly pentagonal. 



Surface of the outer volution marked by rather distant, usually 

 simple, but sometimes bifurcating longer ribs which are prominent and 

 concavely curved on the sides, but feebly <;eveloped, almost obsolete and 

 nearly straight in the flattened siphonal region, at least near to the aper- 

 ture. All of these longer ribs extend to, or commence at, the umbilical 

 margin, and alternate with one or two shorter ones. On the outer portion 

 of the last volution each rib bears two large obtusely conical nodes, one 

 on each side of the periphery or venter, at the ventrolateral angle. 



Sutural line apparently like that of a typical Pachydiscus, as figured by 

 Zittel in the second volume of his Handbuch der Pal?eontologie. 



Comox River, near Comox, V.I., W. Harvey, 1893 : a well preserved 

 cast of the interior of the shell, about four inches in its maximum 

 diameter, the property of the Provincial Museum at Victoria. 



Fig. 23. — Pachydiscus binodatus. — Outline 

 of transverse section of the outer volu- 

 tion, between the ribs and not far from 

 the aperture, of the specimen from the 

 Comox River, represented on Plate 49. 



