STANTON : THE MARINE CRETACEOUS INVERTEBRATES. 39 



There are only three specimens belonging to the species in the collec- 

 tion and they agree very closely except in size and state of preservation. 

 Of the dimensions given below those under I belong to the figured type. 



I II III 



Diameter 250 mm. 210 mm. 300 mm. 



Umbilicus 53 45 62 



Height of aperture 148 113 ^i/S 



Breadth of aperture 72 63 . 94 



The comparisons with described species have already been suggested 

 in the discussion of the genus. It seems remarkable that no young speci- 

 mens of the species were collected and every small ammonite in the col- 

 lection has been critically examined in the hope of finding the sculptured 

 young of this form. The only one that at all suggests such an immature 

 stage is the specimen described beyond as H. tardense, which shows similar 

 sculpture in the umbilicus and even at the diameter of 74 mm. begins to 

 show the disappearance of the ribs, especially on the venter and the umbil- 

 ical wall, but the umbilicus is relatively broader and the sculpture seems 

 too pronounced to permit its reference to this species. 



Locality and position. "Mouth of canon four miles east of Lake Pueyr- 

 rydon ; Ammonite (Belgrano) beds." 



HATCHERICERAS ARGENTINENSE sp. nov. 



PI. IX, Figs. 2-5. 



Shell of about the same form and proportions as H. patagonense but 

 probably not attaining so great a size, the flattened band between the 

 umbilicus and the middle of the whorl somewhat more distinct than in 

 that species ; venter regularly rounded, and smooth on mature whorls ; 

 umbilicus funnelform, nearly one-fourth the diameter of the shell, with 

 rather narrowly rounded or subangular shoulder and smooth walls on 

 adult whorls, but showing distinct, closely arranged ribs in the earlier 

 stages ; surface marked by rather prominent, closely arranged ribs, part of 

 which begin in the umbilicus of young shells up to a diameter of 50 mm., 

 but on later whorls originate on the umbilical shoulder, cross the sides in 

 a gentle sigmoid curve and become swollen but not distinctly tuberculate 

 near the rounded venter, where they are interrupted by a smooth band, 



