NATURAL SCIENCES OF PHILADELPHIA. 445 



A marked feature of this species is the ventricose character of its whorls, 

 which will alone distinguish it from all the others yet known in the Nebraska 

 rocks. As is usual with species marked like this, its revolving lines vary much 

 in their distinctness on different individuals. On some specimens they are well 

 defined, while on others they are nearly or quite obsolete. Usually three or 

 four of those around the middle and upper part of the whorls are larger, and 

 separated by much wider spaces, than those on the under half of the body vo- 

 lution. 



Locality and position, same as last. 



CEPHALOPODA. 



Genus BACULITES, Lamarck. 



Baculites baculcs. 



Shell slender, straight, and gradually tapering; transverse section broad 

 oval, the larger diameter being to the smaller, as 112 to 90 ; surface of septate 

 portion having a few distant, broad, undefined lateral undulations. 



Septa rather distant. Dorsal lobe nearly one-third wider than high, provided 

 with two short, widely separated terminal branches, each of which is ornamented 

 by about four short, digitate branchlets; above these terminal divisions there 

 are on each side two very small lateral branchlets, the upper of which are much 

 smaller than the others, and nearly or quite simple, while the other two are 

 distinctly digitate. Dorsal saddle as long as the dorsal lobe, but scarcely more 

 than half as wide, rather deeply divided at the extremity into two nearly equal 

 irregularly tripartite branches, with short, variously digitate subdivisions. 

 Superior lateral lobe as long as the dorsal saddle, but narrower, and ornamented 

 at its extremity by four short, subequal, palmately spreading branches, each of 

 which has four or five very small, short, unequal branchiets, and a few digita- 

 tions ; above these spreading branches the body of the lobe is comparatively 

 narrow, and provided with a single small digitate lateral branch on each side. 

 Lateral saddle of the same size as the dorsal saddle, and very similarly divided. 

 Inferior lateral lobe broader than the superior, and provided with six short 

 spreading unequal, digitate, terminal branches, of which the three on the dorsa) 

 side are a little smaller than the others. Ventral lobe comparatively large, 

 about twice as long as wide, contracted near the middle, and ornamented at the 

 extremity by seven or eight palmately spreading, nearly equal digitations. 



Our specimen of this species is a septate fragment four inches in length. At 

 its smaller end it measures 0-90 inch in its greater diameter, and 0-70 inch in 

 its smaller do. Its greater diameter at larger end is 1-12 inch, and its smaller 

 do. 0-90 inch. 



This species will be at once distinguished from the Nebraska shell, referred 

 by all authorities to B. ovatus of Say, by its much more rounded form ; indeed, its 

 two diameters are so usually nearly equal, and its dorsal and ventral sides so simi- 

 lar, that it appears almost entirely cylindrical at a first glance, though its sec- 

 tion is a little oval. It has a proportionally larger ventral lobe than B. ovatus, 

 while in all its other lobes and saddles it presents as great differences as are 

 often seen between those of species of this genus. 



In its nearly cylindrical form, it is more like B. Spillmani of Conrad (Jour. 

 Acad. Nat. Sci., Phila., 2d ser., vol. iii,, pi. 35, fig. 24) than any other species 

 with which we are acquainted ; though it is not flattened on the back, nor ob- 

 tusely carinate on its front, (dorsal side,) as in that shell. As Mr. Conrad's 

 specimen does not show the septa, we have no means of knowing whether these 

 forms resemble in their internal characters or not. 



Locality and position. Deer Cre^k, a tributary of the north branch of Platte 

 River. Fox Hills Beds, upper part. 



1861.] 



