126 PALEONTOLOGY OF THE UTPER MISSOURI. 



The synonymy of this genus is involved in some obscurity. We have not been 

 able to consult all the works in which the name was used, between the establish- 

 ment of the binomial system by Linmieus, in his 10th ed. Syst. Nat. 1758/ and the 

 publication of Lamarck's Prodrome, in 1799. Consequently we have no means of 

 determining, beyond doubt, whether or not any of these authors used it in accord- 

 ance with the established usages of the Linnaean nomenclature before Lamarck. 

 It is highly probable, however, that they did not ; and if any of them did, it is 

 more than probable they included both groups — that is, Belemnites, as usually 

 understood, and BeleinnifeUa, D'Orbigny. In the first case, Lamarck would be the 

 first binomial author that used it, and hence the author of the genus ; and in the 

 second case, he would be the first to select the type of the genus. In first using 

 the name in 1799, he gave a diagnosis, but mentions no type or example. In 1801, 

 however, he uses exactly the same diagnosis, and mentions B. pnxillosus (referring 

 to Brcynius's figures) as his only typical example. As this'example, beyond doubt, 

 belongs to the type long afterwards named BelemniteUa, it follows that if we regard 

 Lamarck as the author of the genus, or as the first to select its type, that the name 

 Belemnites will have to be retained for the BelemniteUa group. If so, then Mont- 

 fort's name, Paclites, 1808, would have to be used for the group here described, and 

 tlie name of the following species would have to be written Paclites densus. Not 

 having the necessary works at hand to clear up all these doubtful questions respect- 

 ing the synonymy of this genus, we have concluded to use for the present at least, 

 the generally accepted name Belemnites for this group. 



Belemnites densus. 



(Plate IV, Fig. 10, a, b, c and PI. V, 1, la, h, c. d, e,f, g, li.) 

 Belemnites densus, Meek & Hayden, Proceed. Acad. Nat. Soi. Phila. March, 1858, 58; ib. Oct. 1860, 418. 

 Shell or guard large and thick, suboylindrical, more or less compressed laterally, the cross section having a 

 slightly oval outline. Lower portion tapering to a point ; sometimes a little oblique, usually more compressed than 

 any part above : rarely having, at the immediate point, a narrow, obscure groove on the ventral side, and a very 

 slight carina on the dorsal side. Surface smooth. Alveolar cavity apparently extending about half way down 

 from the summit, and terminating nearly midway between the centre and the ventral side; from this point the 

 axial line passes down, gradually approaching the ventral margin, but curving slightly, so as not to intersect it 

 before reaching the extremity. Phragmocone very slightly curved ; apical angle 20^'. Septa rather closely 

 arranged, about twenty of them occurring in a section one inch in length, measuring 0.72 inch in diameter at the 

 larger end, and 0.35 inch at the smaller extremity ; siphon unknown. 



The most nearly complete specimen of the guard we have seen measures 5 inches 

 in length, and 0.90 inch in diameter at its larger end. The alveolar cavity of this 

 specimen is 2.39 inches in length, and 0.75 inch across at the aperture, which is 

 slightly oval. Some fragments in the collection, however, appear to have belonged 

 to individuals at least one-third larger than that from which these measurements 

 were taken. 



This Belemnite is very closely related, in most of its characters, to B. Panderianvs, 

 D'Orbigny, as figured in Murchison, De Verneuil, and Keyscrling's work on the 

 geology of Russia, vol. 2, pi. 30. The only differences Ave have observed are that 



' Linnajus never adopted Belemnites as a generic name, but merely used it as a kind of specific 

 name, under Helminth olithus, in which he included nearly all kinds of fossils. See Syst. Nat. xii. 

 ed., 1768, iii. 162. Gmelin used it in the same way in xiii. ed. Syst. Nat. iii. 413. 



