JURASSIC SPECIES. 139 



. From another locality in the same region in which the guard described 

 above was obtained, several fragments were bought in, of an elongate-conical 

 chambered shell, that may be the phragmacone of the same or of another 

 Belemnite. It is represented by figs. 8 and 8 a of plate 12, and will be seen 

 to taper regularly from the larger to the smaller end. Its section at all 

 points is very nearly circular, while its septa are deeply concave, and sepa- 

 rated by spaces equaling about one-fifth the greater diameter of the shell at 

 the point of measurement. The siphuncle is very slender, and exactly 

 marginal; surface smooth, or only showing under a magnifier, traces of 

 obscure lines of growth that arch forward on the side opposite the siphuncle. 

 The whole shell must have been, when entire, nearly six inches in length, 

 and, if really the phragmacone of the above Belemnite, it must be evident 

 that that species attained a much larger size than the guards figured would 

 indicate. 



Whether the last-mentioned shell is the phragmacone of a Belemnite, 

 or the shell of an Orthoceras, may perhaps admit of some doubt until better 

 specimens can be obtained ; but that the guard described above is that of a 

 true Belemnite, there can be no doubt whatever. 



Locality and position. — The specimens of the guard are labeled "Cotton- 

 wood Canon, West Humboldt Range", and came, I am informed by Mr. 

 King, from the upper beds of the series, above those containing the Triassic 

 fossils, and are therefore probably of Jurassic (Liassic) age. The larger 

 chambered shell (figs. 8, 8 a) is labeled "American District, West Humboldt 

 Range," Nevada; and probably came from the same horizon. 



