STANTON : THE MARINE CRETACEOUS INVERTEBRATES. 41 



The close agreement in the sutures and in general form and proportion 

 of the shell indicates rather near relationship with Hatchericeras patago- 

 nense, while the more pronounced and more persistent sculpture of this 

 form serves to distinguish it specifically. Even if additional collections 

 should prove that large old specimens become smooth, such specimens 

 can be at once distinguished from H. fiatagonense by the finer, more 

 closely arranged ribs on the earlier whorls, as shown in the umbilicus. 



This species, especially in its immature stages, has many features in 

 common with Hoplites and should probably be included in that genus as 

 broadly defined in Zittel's Handbuch to include several diverse groups, 

 but these resemblances are believed to indicate family relationship and the 

 probable immediate ancestry of the new genus here proposed. 



Localities and position. One specimen (the largest collected) with the 

 preceding species from the " mouth of cafton, four miles east of Lake Pueyr- 

 rydon" and about twelve more or less fragmentary specimens, mostly 

 young, from "ten miles east of Lake Pueyrrydon," all from the Ammo- 

 nite (Belgrano) beds. 



HATCHERICERAS? TARDENSE sp. nov. 



PI. X, Figs. 3-5. 



Shell rather small, compressed, moderately involute, the umbilicus meas- 

 uring about one fourth the diameter of the shell ; sides of the whorls 

 slightly convex, venter regularly rounded, becoming smooth on mature 

 whorls ; surface marked by rather prominent and distant, slightly sinuous 

 ribs, that mostly spring in twos and threes from well-marked tubercles on 

 the rounded umbilical shoulder, with occasionally one or two shorter 

 interpolated ribs between the groups of longer ones ; ribs more prominent 

 on the earlier whorls, where they cross the venter without interruption and 

 tend to form tubercles on either side of it. The outer half of the last 

 whorl of the type specimen shows a gradual weakening of the ribs and 

 tubercles, the sculpture disappearing entirely from the venter and the um- 

 bilical slope near the aperture. 



The suture drawn from the middle of the last volution is of the same type 

 as in the two preceding species but somewhat less complex in its details, 

 probably on account of immaturity of the specimen, which is small and 

 septate throughout. (In the figure the inner part of the suture beyond the 



