CErHALOPOIU. 



There were at least three kinds of pro-ostracum in the 

 family Belemnitidce. 



A. In many Belemnites the extension of the conotheca seems 

 to run out in one simple broad plate, Fig. 3, as in B. hastatns 

 from Solenhofen. 



B. In Belemnites Puzosianus, D'Orbigny, the pro-ostracum is 

 very thin, and apparently horny or imperfectly calcined in the 

 dorsal region, supported laterally by two long, narrow, parallel, 

 calcareous plates, Fig. 4, as in B. Puzosianus from the Oxford 

 clay. Professor Huxley considers this difference between the 

 pro-ostraca of generic importance. 



C. The third kind of pro-ostracum is exhibited by Orthocera 

 elongata, De la Beche, the type of the genus Xiphoteuthis, 

 Huxley ; it is calcareous, and is composed of concentric lamellae, 

 each of which consists of fibres disposed perpendicularly to the 

 plane of the lamella ; the phragmocone is very long and narrow, 

 and the guard cylindroidal. 



Professor Huxley suspects that a thoroughly well-preserved 

 specimen of Belemnoteuthis will some day demonstrate the exist- 

 ence of a fourth kind of pro-ostracum among the Belemnitidce. 



The genera in the family are : — 1, Belemnites ; 2, Belemnitella ; 

 3, Xiphoteuthis ; 4, Belemnoteuthis ; 5, Plesioteuthis ; 6, Celceno ; 

 1,Behptera; 8, Belemnosis ; 9, Conoteuthis ; and? Helicerus. 



• ' The A anthoteuthes of Munster, so far as they are known 

 only by hooks and impressions of soft parts, may have been 

 either Belemnites, or Belemnoteuthis, or Plesiotcuthes, or may have 

 belonged to the genus Celceno." (Huxley.) 



The genus Belopeltis, Yoltz, was founded on the pro-ostraca 

 of Belemnites, species of which were unknown. 



The genus Actinocamax, Miller, was founded on the guard 

 of Belemnites and Belemnitella, the upper parts of which had 

 decayed, and thus presented no alveolar cavity. 



Order II.— Tetrabranchiata. 



Family I. — Nautilltle 

 (including Family II. — OrthoceratlDjE). 



Division a. — Air-chambers confined to one part of the 

 shell. 



Ascoceras, Barrande, 1846.* 

 Etymology, as7cos, a leathern bottle, and ceras. 



* At p. 185 Mr. Woodw<ard refers to M. Barrande's second volume of the " Cephalo- 

 poda of Bohemia." The Ascoras, Glossoceras, and Aphragmites are here described. 



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