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I have also examined another young specimen of a different spe- 

 cies of this genus which has a much larger umbilical perforation, 

 but is otherwise quite similar in the characteristics of the nepionic 

 stage. The contact furrow begins in this specimen with a very 

 slight impression late in the neanic stage and the tubercles appear 

 earlier than in Temnocheilus subtuberculatus. 



Temnocheilus subtuberculatus. 



Nautilus subtuberculatus, Sandb. (Verst. Nass., PI. xii, Fig. 3). 

 PL x, Figs. 27 and 28. 



The umbilical perforation is large and open (Fig. 27, PI. x). 

 The nepionic stage has the first apical chamber very deep. The 

 first suture has the usual ventral saddle and lateral lobes, but on 

 the dorsal side there is a well-defined dorsal saddle. The apical 

 chamber and the inner parts from the second to the fifth are coated 

 with calc spar, while the centre is filled with iron pyrite. 



The second suture has a dorsal lobe in place of a saddle and this 

 persists in later stages. In the paranepionic substage a digonal 

 whorl is developed and the lateral saddles appear dividing the late- 

 ral lobes from ventral lobes that replace the ventral saddles of the 

 metanepionic substage. Contact takes place in the metaneanic or 

 paraneanic substage after the digonal whorl has been replaced by a 

 trapezoidal outline. 



The form of the whorl soon after contact is shown in Fig. 28 and 

 this has the adult outline with the exception that the contact furrow 

 and the tubercles have not yet made their appearance. 



This description was taken from a specimen in coll. Museum of 

 Comparative Zoology, from the lower Devonian of Wissenbach. 



Metacoceras. 



This genus, which has been described in my Genera of Fossil 

 Cephalopods (p. 268), and subsequently redescribed in "Carbonif- 

 erous Cephalopods," Second Annual Report of Texas, 1890, and 

 Fourth Annual Report of Texas, 1892, is of no special value in this 

 connection except as an illustration of a number of genera of the 

 same genetic stock as Temnocheilus, which have more or lesss 

 similar characteristics in the young. They all have large umbilical 

 perforations and a similar history in the development of the im- 

 pressed zone. 



