480 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



Hctcrocerns! Nebrasccnsc, M. & H. 



Plate 22, ligs. 1, a,l>,c. 



Ancyloceras ? Nebrascense, Meek and Hayden (1836), Proceed. Acad. Nat. Sci. Philad., VIII, 71. 



Turrilites Nebrascensis, Meek and Hayden (1850), il>., VIII, 280. 



Helieoceras ? Xebrasccnsc, Meek (1H04), Smithsonian Check-List N. Am. Oct. Fossils, 2."). 



Our specimen of this species consists of about the half of one volution, 

 and measures near 2.80 inches in length around the outer side. It is sub- 

 cylindrical, or tapers but slightly, its diameter at the larger end being about 

 one inch, and at the smaller extremity 0.95 inch, and forms a short dextral, 

 spiral curve, so as to leave an umbilical cavity within, equaling the greatest 

 diameter of each surrounding whorl. The volutions seem to have been 

 in contact, and are ornamented by small annular costae, which pass very 

 obliquely around, and sometimes appear to bifurcate on the outer side, where 

 there are some remains of small nodes. The siphuncle occupies the middle 

 of the outer side, and is quite small. 



The specimen is unfortunately not in a condition to show all the rami- 

 fications of the lobes and sinuses ; but they are seen to be very complex, and 

 do not differ materially in size or form on opposite sides of the whorls. The 

 siphonal lobe is longer than wide, and has two principal branches on each 

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

 subdivided into two or three unequal, sharply digitate branchlets ; the other 

 two principal branches are opposite, spreading, and bifurcated ; one of the sub- 

 divisions of each being larger than the other, and armed by about seven or 

 eight sharp digitations. The first lateral lobe is a little longer and much 

 wider than the siphonal lobe, and very deeply divided into two great spread- 

 ing, variously subdivided, and sharply digitate branches. The second lateral 

 lobe seems to be rather smaller, but, as far as can be determined, very simi- 

 lar to the first; while the antisiphonal lobe is comparatively large, though 

 slender, and tripartite at the extremity, the middle division being largest, 

 bifurcating, and, like the other two principal divisions, variously digitate. The 

 details of the sinuses are not clearly visible in our specimen, though the 

 third lateral one on both sides of the whorls is very deeply divided by a 

 large auxiliary lobe. 



This species will be readily distinguished from either of the foregoing, 

 even when found in fragments, by its smaller umbilical cavity in proportion 

 to the diameter of its whorls', as well as b_v the differences in its septa. It 

 seems to have had, like most of the species, two rows of nodes around the 



