50 



can Philosoi^hical Societj', Vol. XXXII, p. 525. Tbo genus was 

 founded on a fragment of a cast from an unknown locality and 

 named 7i*. imprci<:<iim. If we are correct in referring our species to 

 his genus, it will serve to fix tlie geological range of his species and 

 po.ssibly point toward the locality. f)ur specimen is from w'hat is 

 called by the local collectors, in Indiana, the Knobstone (iroup, 

 which is not very definite, liut means the Keokuk Group and the 

 Waverly. wlicic the two arc not separnVilc. and the fossils are gener- 

 ally casts. 



Our species is larger tlinii the lype. NOIiit ions niinuTous. I'ni- 

 bilicus wide and showing almost completely cadi inner tnrn. and 

 probably perforated. The rajiid enlargement of the ])art preserved 

 indicates a complete perforation. Transxerse section subelliptical. 

 The ends in fig. 2 are altr)gi'th('r too round, a V)etter idea of tlu^ 

 subelliptical section will lie formed liy coinparing figs. 1 and 2 or 

 figs. 2 and 3. It is the way the t^nds are fractured that gives this 

 erroneous outline in fig. 2, drawn under a camera lucida. The 

 ventral side is depressed convex, witli a suhajigidar ventro-lateral 

 ridge on each side. Lateral sides narrowly ronndcd toward the 

 umbilicus. Dorsal side has a slightly concave depression or contact 

 furrow, a little less than one-third the lateral diameter of the shell. 

 The sutures have broad ventral and lateral lobes with saddles ven- 

 tro-laterally and at the rommcnci'ment of the niiibilicns. or they 

 might be said to be indicated l)y a waving line. Irlach one forms, 

 however, a V-shaped angle in the dorsal sinus or contact furrow. 

 The septa are distant on the ventral side about <inc-half the dorso- 

 vcntral diameter. At the small end of our specimen they are 

 distant a little less than half the dorso-ventral diameter and at the 

 larger end a little more than half the dor.so-veidral diameter. The 

 outer shell is unknown. 



Found by G. K. (xreene. in the Knobstone G-rou)). at Sampson 

 Springs, in Clarke county. Indiana, and now in the collection of 

 Wm. F. E. Gurley. 



