496 
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 Zemnochetlus subtuberculatus. 
TEMNOCHEILUS SUBTUBERCULATUS. 
NAUTILUS SUBTUBERCULATUS, Sandb. (Vers¢. Vass., Pl. xii, Fig. 3). 
Pie x. ehigs. 27° and 28. 
The umbilical perforation is large and open (Fig. 27, Pl. 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paraneanic substage after the digonal whorl has been replaced by a 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 Zodlogy, 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. 
