BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 413 



the camera between the septal necks (appearing in plate 4, figure 3, 

 as tonguelike processes and noted more fully under V . o p p 1 e - 

 t u m ) in one species of Vaginoceras suggests that we might have 

 here a condition like that represented by Hyatt in the above men- 

 tioned diagram, where each sep- 

 tal neck extends only to the next 

 preceding one and supplementary 

 pieces are intercalated between 

 the adjoining septal necks. Hyatt 

 has not mentioned this structure 

 in the text, as far as I am aware 

 and I have here [see text fig. 3] 

 reproduced an enlargement of 

 a portion of the drawing in 

 question to bring out more dis- 

 tinctly this peculiar structure. 



Since the species here referred 

 to Vaginoceras shows in some 



parts of the section distinctly the continuation of the septal necks 

 though in others it might easily lead to a reconstruction of the 

 siphuncular wall like that given in the diagram of Endoceras 

 proteiforme, I have preferred to adopt the former view as 

 the simpler one and as the one more liable to be correct. 



Fig. 3 Endoceras proteiforme H; 

 (Copy from Hyatt) 



Vaginoceras oppletum sp. now 



Plate 4, figure 2, 3 ; plate 5, figure 1-4 ; plate 6, figure 1 ; plate o, figure 1-3 



Description. Large orthoceracone which must have attained a 

 size of 1 m and more. Imperfect specimens 45 cm long and with 

 a diameter of 10 cm, which at the rate of growth of this species 

 would correspond to a length of 120 cm, have been observed. The 

 rate of growth is very slow (one conch was found to expand 10 mm 

 in the distance of 117 mm, or 1 in 12; another 6 in 57 mm) and de- 

 creases slightly with advancing age. The section of the conch is 

 subcircular or but slightly elliptic (major and minor diameters 58 

 and 51 mm; respectively 55 and 50 in another, but from the ellip- 

 tic sections of the siphuncles in these specimens it is probable that 

 the conchs are slightly compressed). The living chamber attained 

 a large size but its proportions are not fully determined owing to 

 the imperfection of the specimens. The aperture is unknown. 



The cameras are shallow, slightly and regularly increasing in 

 depth to the living chamber, there being counted four in the space 



