106 



Report of the State Geologist. 



Sandbergerogeras syngonttm, sp. nov. 



Plate VII, Figs. 19, 20. 



Shell widely umbilicated, with broad and shallow whorls. At maturity 

 six or seven whorls are exposed and the umbilication at this stage equals 

 nearly one-half the diameter of the shell. In cross-section the mature whorl 

 is considerably wider than high, and the inner w horls have this difference 

 greatly increased. The venter is broadly flattened by a duplicate keel, 

 which covers one-half or the entire lateral width of the whorl. This 

 hyponomic area consists of a median convex portion and two very narrow 

 lateral grooves from which it is distinctly separated by a narrow elevated 

 line. Each of the lateral furrows is separated from the sides of the whorl 

 by an elevated ridge. 



Ornamentation. Upon the innermost whorls are sharp, elevated con- 

 centric lines, which soon become united in small bundles, so that the costate 

 appearance of the whorls shows itself as early as the third volution. Out 

 ward, the size of the bundles increases; on the fifth whorl they begin to 

 modify the surface of the shell itself, and on the final whorls they become 

 ridges, bearing fine, elevated striae upon their surface and in the interspaces. 

 These ridges or costae have a sigmoid curve, bending forward toward the 

 venter, but they become less prominent the further they retreat from the 

 umbilicus, and on the ventral surface are wholly resolved into striae. Upon 

 reaching the hyponomic area, the striae are sharply recurved over the 

 Lateral grooves and continued backward in deep hyponomic festoons over 

 the median area. 



Early characters. The protoconch of this species is very large, much the 

 largest of any of the Devonian forms here described; it is ovoid and its 

 lateral extremities project conspicuously beyond the margins of the median 

 and later portions of the first w horl. 



It declines in size from its posterior extremity forward, and our material 

 show s that after the appearance of the first septum there is a gradual loss in 

 diameter in the first whorl followed, after minimum diameter is attained, 

 by a slower gain in width. The overlap of the conch upon the protoconch is 

 hence, less at the middle or even at the end of the first whorl than at its 

 beginning. This is evidence quite similar to that observed in more fully 

 represented species, Montic. Pattersoni, Probel. Ltithen', etc. 



