80 University of Texas Bulletin 



The coiled portion consists of an unknown number (3 or 4 ?) volutions, 

 and the umbilicus is deep and, due to the position of the dorso-lateral 

 tubercle, has a kidney-bean shape with the end nearer the aperture some- 

 what pointed. There is a distinct elongation, which in the absence of 

 the uncoiled portion will orient the shell. 



For the most part there are no sutures nearer the aperture than the 

 dorso-lateral tubercle, and the uncoiled portion represents the living 

 chamber, and therefore lacks sutures. 



Coiled portion ventricose to subglobular, very obese, subovate in out- 

 line, evenly and almost circularly rounded ventrally ; dorsally the circular 

 margin is broken by the incurved margin of the dorso-lateral tubercle, 

 resulting in a more or less open crescentic or tear-shaped umbilicus, lying 

 slightly oblique to the axis of the uncoiled portion; greatest transverse 

 diameter of coil ventral to this tubercle; coil slightly constricted just above 

 the tubercle. The uncoiled portion of which the part below the tubercle 

 is the living chamber, is elongate and ornamented with numerous fine 

 ribs which course obliquely from the dorso-lateral margins to the venter, 

 being nearer the aperture at the latter point. The living chamber is in- 

 flated at the edges at the dorso-lateral tubercle where it is in contact, 

 with the coil, constricted dorsally at a point a little nearer the aperture 

 and thereafter on approaching the aperture is constricted and curved 

 dorsally. Its dorsal side is excavated into a prominent groove, whose 

 width is about half that of the living chamber, and into which the coil 

 fits at the upper end; the groove thus is exposed from the coil to the 

 aperture. The resulting cross section of the living chamber is concave- 

 convex, the short dorsal concave margin passing over the sharply rounded 

 edges of the dorsal groove into the longer lateral and ventral margin. 

 This section varies at different points of the scaphite; near the aperture 

 it is more concave dorsally. 



FORM : There is a variation in form, amount of embracing and rate 

 of increase in size of the successive volutions, as is seen also in the inter- 

 grades between Scaphites obliquus and Scaphites aequalis. 1 



The type of Scaphites hilli is an obese individual with thick, rapidly 

 expanding volutions, which closely approaches the typical S. aequalis 

 Sowerby as figured by Pervinquiere. This expansion over the last volu- 

 tion of the coil amounts to a doubling of the breadth of the coil, the 

 breadths at the dorso-lateral tubercle and at the point opposite it on the 

 next volution being in the ratio of 8:3.6 in the type. The amount of 

 thickening interiorly is also great, since the umbilicus is deep. The re- 



'Pervinquiere, Et Pal. Tun., pp. 118-120. 



