BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLATN BASIN 461 



g i n i a n 11 s ; at end of 2^ volutions, 2 J^ cameras against 3^ 

 in E . V i r g i n i a n u s ) and the amount of involution ; in E . v i r- 

 g i n i a n u s the volutions being hardly impressed on the dorsal 

 side. 



Unfortunately our material does not permit to trace the ontoge- 

 netic development of this form which probably would present in- 

 teresting facts. 



E. accelerans possesses in fragments some similarity with 

 Tarphyceras champlainense Whitfield ( sp. ) . It can, 

 however, in such examples still readily be distinguished by the 

 greater rate of expansion and more convex venter. 



Eurystomites amplectens sp. nov. 



Plate 18, fig-. 4-7 



Description. Conch a closely coiled nautilicone (also in gerontic 

 age ?) of three (or more) volutions; of moderate size, a conch of 

 three volutions having a diameter of about 70 mm. Volutions sub- 

 circular in nepionic and neanic stages, in ephebic stage reniform with 

 a higher and narrower ventral region [see pi. 18, fig. 4]. Ven- 

 tral zone indicated on ephebic whorl by a slight flattening; the im- 

 pressed zone appearing on first whorl and increasing steadily in 

 depth to living chamber. Involution considerable, increasing steadily 

 (one fourth within first whorl, one third of second whorl projecting 

 on first, one half of third on second). Growth of conch uniform, 

 rapid, the hight doubling ( 16 to 32 mm) within the last volution. 

 Umbilical opening extremely small or absent. 



1 X vol. 

 1vol. 



Fig. 24 Eurystomites amplectens sp. nov. 

 Sutures x ^ 



Length of living chamber and character of aperture unknown. 

 Cameras shallow, 3^ being counted within the space of 20 mm on 

 the ephebic whorl (counting along the middle of the lateral side). 

 Septa possessing considerable convexity, being about as deep as the 

 cameras ; sutures straight transverse in the nepionic stage, with very 

 low ventral saddle and shallow lateral lobe in neanic stage, broad 

 and high ventral saddles and corresponding deep lobes in the ephebic 

 stage, where the sutures also arch strongly forward near the line of 



