518 
OPHIDIOCERAS TESSALLATUM. 
OPHIDIOCERAS TESSALLATUM, Barrande (Sys¢, S7Z., Pl. xlv) ; Pl. viii, 
Figs. 26-28. 
Loc., Bohemia. 
The specimen, Fig. 28, Pl. viii, showed the metanepionic sub- 
stage with the usual two septaand 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 anothér 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 ccecal 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 rudens. 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 costa seemed also to be accelerated in some specimens. 
Fig. 27, Pl. 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. 
Rutoceratide. 
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, Kophiniocees 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 Cephalopods, p. 284, and associated 
