FOURTH, OK < .>i;. RH \\, h 



173 



with entire lateral ridges, which occupy nearh the whole breadth of the abdomen. 



1 iriance with bis description <>m this point, and may 



taken from different whorls; one in Volume V. baa narrow channels, 



while the section in Volume IV. Plate XVI. has broad chi nek I in- section, 

 ption, and sutures shon lateral distortion. If it were not for this and the 

 • • errors of tin' figures, we should be positive that it was a tuberculated 



arnioceran form. 



Arnioceras Humboldti, Htati 

 Uomboldl i • . 



Tli - :u»in which, however, it differs 



in the sutures and proportions of the whorls, those of the latter being broader in 

 proportion to their breadth. This species also probably reached a larger avi 



nd had ■ thicker shell It difl 

 from same charac- 



snd the - less divergent 



outwardly than in that Bpecies,and not 

 so flat The great thickness of the 

 shell reminds one of Am. ffarfnuumi, 

 but the whorls increase faster by 

 rth in the abdotni no-dorsal diame- 

 ter, and it has a smaller number <>f 



whorls at the 



:<> the natural Bize, and i 

 . the proportions of the fu- 

 sil. The actual diameter of the fi 



represented in 

 nun. and the keel is a trifle mure prominent than it appears in the drawing. 

 Tin- pUaa were much abraded and are truthfully portrayed in this figure, hut 

 when eiirue t|,e\ j ,« , — . — , -. l the usual sharpness of the genus A 



I tion represented in Figure •"«'_' is in pari a restoration, and 



en slightly reduced in thi ["he extreme breadth of the Bide and keel 



■ mm. The sutun n with sufficient accuracy in I it the 



n lobe which divides the superior literal saddles has been overlooked, and 



luminal 1 ol I n indicated The latter has the usual arm. 



tmewhat shorter than the superior laterals The mat 

 lividing t ; or lateral saddles is unusually broad, and in fact the 



l <>f the two I marked ■ 



■ 



In the collection of the Mining Bui ,l "'" 



of At • h hich, judging from a I It 



I 'ollllt\ . ( I. lit We M • 



It is, however, ' 



: in the West in tie pied by ' ; 



