PALAEONTOLOGY OP THE UPPER MISSOURI. 



merely digitate; above these there is on the dorsal side one digitate lateral branch, 

 and on the ventral side one or two lateral digitations. The lateral saddle is much 

 smaller than the dorsal saddle, more or less oblique, and ornamented at the extremity 

 by some five or six very short, palmately spreading, obtuse divisions. The inferior 

 lateral lobe is as wide, but scarcely half as long, as the superior, and on one side of 

 the shell divided to its very base into two small, nearly equal, digitate parts; while 

 on the other side of the shell it is narrower, and tripartite. Between this and the 

 umbilicus there are about three very small, rather distant, digitate ventral lobes. 



This species is quite distinct, in the structure of its septa, from all the other 

 Ammonites yet known in any of the Nebraska rocks, and we are not acquainted 

 with any nearly allied forms amongst foreign species. The only specimens of it we 

 have seen are somewhat distorted, and consist of the inner septate whorls. One 

 of these measures 3.10 inches in its greatest diameter, and 1.33 inch in breadth. 



The specific name was given in honor of Prof. Joseph Henry, Secretary of the 

 Smithsonian Institution. 



Locality and position. Southwest base of the Black Hills, in the upper Jurassic 

 rocks of that region. (No. 314.) 



ORDER Dihraiicliiata. 



SUBORDER DEC APOD A. 



FAMILY BELEMNITIDJS. 



Shell (internal) consisting of a somewhat nacreous pen, expanded in 

 front, and terminating posteriorly in a thin chambered cone, with simple 

 septa, called the phragmocone, which is sometimes enveloped in a strong 

 subcorneous or calcareous guard, having a radiated semi-fibrous struc- 

 ture. Chambers of the phragmocone connected by a ventral siphon. 



Although this family is entirely extinct, specimens of one of the genera (Belem- 

 noteuthis} have been found in such a state of preservation as to give a tolerably 

 correct idea of the softer parts of the animal. From these it has been ascertained 

 that it was provided with arms and "tentacles of nearly equal length, armed with 

 corneous hooks. The mantle was free all around, and the fins medio-dorsal. 



This family embraces the genera Belemnites, Xiphoteuihis, Belemnitella, Acantlio- 

 teuthis, Belemnoteuthis, Conoteuthis, and Helicerus. 



Genus BELEMNITES, AUCT. 



Kynon.Belemnites, LISTER, 1678, and (in whole or part) of various other pre-Linntean authors. SCHEOTEB (part ?), 

 Lith. Lext. 1779, i. 151 ; Vollst. Einl. 1784, IV, 149. ROISSY (part), Moll. V, 1805, 43. CCVIEE (part), 

 Regn. An. 1817, 371. D'ORBIONY, Palaeont. Fr. Ter. Cret. 1, 1840, 37 ; An. Sci. Nat. XVII, 1842, 241 ; 

 Moll. Viv. Et. Fo?s. I, 18 ** ?, 459 aud of many later writers. (Not Belemnites, LAMARCK, Prodr. 1799, 

 81 ; nor Syst. An. 1801, 104; nor An. Sans Vert. 1822, VII, 590, which is Belemnitella, D'ORBIONY.) 



Paclites, MONTFORT, Conch. Syst. I, 1808, 318. 



f Thalamus, MONTP. 1808, ib. 322. 



Achelois, MONTF. 1808, ib. 358. 



Callirhce, MONTF. 1808, ib. 362. 



Cetosis, MONTF. 1808, ib. 370. 



Acamas, MOXTF. 1808, ib. 374. 



? Chri/saor, MONTF. 1808, ib. 378. 



Hibolithes, MONTF. 1808, ib. 386. 



