﻿518 



Ophidioceras tessallatum. 



Ophidioceras tessallatum, Barrande (Sysf. Si/., PL xlv) ; PI. viii, 

 Figs. 26-28. 



Loc, Bohemia. 



The specimen, Fig. 28, PI. viii, showed the metanepionic sub- 

 stage with the usual two septa and long apical chamber, but internal 

 to the first septum there was on the venter internal dark lines, indi- 

 cating a subventran siphuncle. This was cut off by another dark 

 line which may possibly have been the fragmentary remains of a 

 septum. Nevertheless there was no positive proof of this and the 

 question must still be left open. The usual circular mark occurs, 

 indicating the coecal termination on the worn apex in a subventran 

 position. In the second septum the siphuncle is extracentroven- 

 tran. ■ 



The formation of the ventral zone began earlier in this species 

 than in Ophidioceras mdens. The flattening of the abdomen began 

 even in the paranepionic substage and in the ananeanic substage 

 the formation of the zone was well advanced. The development of 

 the costse seemed also to be accelerated in some specimens. 



Fig. 27, PI. viii, shows the contact furrow as it first appears when 

 crossing the apex. Fig. 27 shows that the umbilical perforation is 

 larger in this species than the others described here, since the first 

 whorl does not meet the ananepionic substage on the dorsal side 

 but strikes it on the surface of the apex, ventrad of the centre. 

 The contact furrow is consequently not at first so deep as in other 

 species, unless this characteristic is variable. 



Rutoceratidoz. 



This family consists of a number of genera which are interesting 

 in connection with the history of the impressed zone only in so far 

 as they show that this peculiarity is correlated with close coiling, or, 

 in other words, is due to contact. 



Thus, Zitteloceras, Halloceras, Rutoceras, Kophinoceras and Stro- 

 phiceras as a rule do not have the whorls in contact and do not 

 have an impressed zone. The shell in most of these is a rough 

 imbricated structure with ridges or nodes arising from the greater 

 or less permanency of the frilled projections of the apertures. 

 These genera, found in the Silurian and Devonian, were described 

 in my Genera of Fossil Cephalofiods, p. 284, and associated 



