422 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



This character is also well marked in a European specimen of that shell now 

 before me. In the Wyoming specimens, however, nothing of this kind is 

 seen ; the lip, on the contrary, being abruptly beveled, without the slightest 

 traces of a njarginal rim. This I have ascertained to be the case, not merely 

 from examining internal casts, but from seeing, in one instance, a portion of 

 the shell itself remaining at the edge of the lip. 



Farther comparisons also show the following additional external differ- 

 ences. In the European specimens of S. aqualis, the body-portion, just at 

 the point where the last septum crosses, becomes abruptly more ventricose, 

 and continues so on nearly to the aperture, where it again contracts some- 

 what. In the Wyoming form, however, this is not the case, the body-part 

 only increasing in size regularly in proportion to the increase of the inner 

 turns. Again, the costae on the periphery of the Wyoming shell are all quite 

 distinctly larger and more distant, and likewise differ in becoming regularly 

 larger and more distant to, and beyond, the middle of the body-portion, and 

 then again smaller and more closely arranged toward the aperture. But, on 

 the periphery of European specimens of S. cequalis, they are larger and less 

 crowded some distance behind the position of the last septum, and become 

 smaller and more crowded to a little beyond the point where the body-part 

 suddenly assumes a more ventricose form, where they are so very fine and 

 close together as to leave only faint traces on internal cast; then beyond 

 this they become gradually larger and more distant on to the aperture ; 

 near which they are larger and less crowded than on any other part of the 

 periphery. 



The only illustration of the septa of 8. cequalis I have seen, is that given 

 by d'Orbigny in vol. I, Pale'ont. Fr., pi. 129. On comparing our cut of a 

 septum of the Wyoming shell, it will be seen that the latter has its principal 

 lobes and sinuses much more simple, and its smaller lobes much narrower and 

 more prominent. I should remark, however, that the septa of the European 

 specimens of S. aqualis, now before me, agree more nearly with those of the 

 Wyoming shell than d'Orbigny's illustration of the same does, though still 

 differing in the more slenderly branched and digitate nature of the siphonal 

 and first lateral lobes, as well as in some other details. 



From all the means of comparison within my reach, I am inclined, for 

 the reasons already mentioned, to regard the Wyoming specimens as repre- 

 senting only a variety of S. Warreni, and at the same time very closely allied 



