488 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



ascending spiral curve, in such a manner that if continued around, there would 

 be left between the whorls a free space apparently equal to their own breadth, 

 and an umbilical opening within more than three or four times the diameter 

 of each whorl. The siphuncle is quite small, and passes around a little above 

 the middle of the outer side. The surface is ornamented by rather irregular, 

 moderately distinct, annular costae, which occasionally bifurcate, and extend 

 nearly straight around the whorls. On the outer side, they are stronger than 

 within, and show a disposition to develop small nodes. 



Septa rather complex ; siphonal lobe not more than half as long, and 

 about half as wide as the first lateral lobe, with two principal divisions on 

 each side, the two terminal of which are much larger than the others, and 

 each distinctly bifid, with digitate margins ; first lateral sinus longer than the 

 siphonal lobe, but much more contracted at its base, very oblique, and at its 

 extremity divided into two unequal, spreading, branched, and digitate sub- 

 divisions ; first lateral lobe very large, and deeply divided into two great, 

 spreading branches, with each four or five unequal, digitate smaller divisions ; 

 second lateral sinus much like the first, excepting that it is not oblique ; 

 second lateral lobe a little smaller, but in other respects scarcely differing 

 from the first ; third lateral sinus smaller, though much like the first, with 

 its obliquity in the opposite direction ; antisiphonal lobe about as long, and 

 near half as wide as the siphonal, and tripartite at the end, with more or 

 less digitate margins. 



The fragmentary condition of the specimens of this shell that have been 

 found, is not altogether satisfactory in regard to its generic characters, 

 though they clearly show that it was not coiled in a plane, as in Hamites and 

 Ancy/oceras, but spirally curved as in Helicoccras. On comparison with the 

 typical species of H. Morton?, our shell will be seen to agree pretty nearly 

 in form and size, but seems to make a somewhat shorter curve. In I he 

 details of the lobes and sinuses of its septa, there are also some differences, 

 particularly in the form and mode of division of the antisiphonal lobe. These 

 differences at one time led to the conclusion that it was a distinct species, 

 and, if constant, would certainly warrant its separation under another spe- 

 cific name. As further examinations, however, show it to vary more or less 

 in the details of its lobes and sinuses, particularly those of the antisiphonal 

 lobe, which in some cases shows a tendency to assume the form of that of 

 the typical H. Mortoni, I have elsewhere ranged it under that name; and, 



