314 SYSTEMATIC PALEONTOLOGY 



SlNUITES GRANISTEIATUS (Ulrich) 



Plate LV, Figs. 9-11 ; Plate L, Figs. 40, 41 



ProtowartMa granistriata Ulrich, 1897, Minnesota Geol. Survey, Pal., vol. 

 iii, pt. 2, p. 870, pi. Ixiii, figs. 28-30. 



Description. " Shell scarcely reaching the medium size, closely coiled, 

 leaving no umbilicus; center of dorsum raised into a low broad ridge, 

 defined on each side by an obscure wide furrow; with age the outer 



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boundaries of the latter increase gradually in distinctness, the back of the 

 outer half of the last volution in the largest specimens presenting a 

 flattened appearance ; but the central ridge, though decreasing somewhat 

 in hight, continues to the aperture. In casts of the interior there is a 

 small umbilicus, while the central ridge is nearly as on the shell itself. 

 Aperture transverse, about twice as wide as high, the width generally 

 equalling the hight of the shell; sinus wide, only moderately deep, the 

 margin of the lobes bending rather sharply where the apertural margin is 

 intersected by the faintly raised boundaries of the flattened dorsum. 

 Except in the umbilical regions the test is thin. Out of nearly 30 speci- 

 mens,, only two preserve anything of the external layer. These show that 

 it is marked by fine lines of growth and by very delicate revolving lines. 

 All of the other testiferous examples preserve only the inner and middle 

 layers, the latter appearing in every case quite smooth. Most of the 

 specimens preserve what may be called a fourth layer. This seems to 

 have been deposited by the inner mantle over the inner volutions, includ- 

 ing the smaller half of the outer, while on each side it extends around the 

 callous filling of the umbilicus. The whole of this layer is finely granu- 

 lose, except the lateral extensions, and these are covered by wavy revolving 

 striae. Hight of an average shell, !19 mm.; width of aperture, 19 mm.; 

 median hight of same, 9.3 mm. ; width of inner volution, 6 mm. ; depth 

 of sinus, 5 mm. ; width of same, about 10 mm." Ulrich, 1897. 



This shell is related to the preceding Sinuites cancellatus, but the latter 

 species has a deeper sinus, a rounder back and no dorsal ridge nor obscure 

 furrows. When well preserved, the difference in surface markings is also 

 a distinguishing character. 



