434 
The young become almost as close coiled during the paranepionic 
substage as in Trocholites, differing in this respect from those of 
Eurystomites. The dorsal furrow appears in some species, perhaps 
in all, in the paranepionic substage. This might be considered as 
due to the quick growth and contiguity of the whorls, the dorsum 
of the paranepionic substage being brought close to the dorsum 
of the preceding metanepionic and ananepionic substages of the 
first whorl. ‘This extraordinary condition of the first whorl obtains 
also in Trocholités and will be discussed more fully under the head- 
ing of Zarphyceras prematurum and Trocholites. I do not intend, 
here or elsewhere, as has been stated in other parts of this paper, to 
express a positive opinion that the dorsal furrow in any of these 
nautilian forms was originated in the nepionic stage by the mechan- 
ical stress of the metanepionic dorsum even in these very closely 
coiled shells. The evidence that this may have been the cause is 
not satisfactory, nor is there any positive evidence of an entirely 
satisfactory character that the dorsal furrow was genetic. 
The siphuncle is centren in the ananepionic substage, but becomes 
quickly propioventran and continues near the venter for a more or 
less prolonged period, shifting slowly towards the center. In 
Eurystomites this shifting usually takes place later, or does not 
occur at all, and the siphuncle is larger. 
The septa are less convex usually than in Eurystomites and, as a 
rule, more numerous in each volution. 
The sutures have well-marked lateral lobes and have broad sad- 
dles on the venter. This ventral saddle may be rounded or straight 
or have a slight shallow depression or lobe in the median line. The 
sutures, as they approach the lines of involution, are usually more 
inclined forwards towards the umbilicus than in Eurystomites. 
The whorl in section has a flattened venter and frequently slightly 
flattened zones on the sides, so that there is often a decided approxi- 
mation to the quadragonal form. 
The living chamber is somewhat over one-half of a volution in 
length. The aperture is like that of Trocholites, with a deep, broad 
hyponomic sinus encroaching upon the lateral zones, these last being 
bordered by broad crests, with slight sinuses at the lines of involu- 
tion. ‘There appears to have been a slight crest on the dorsum. 
The lines of growth are parallel with the borders of the aperture. 
_ The shell usually has strong striz of growth externally, but no 
costations ; there are only the broad, slight ridges following the 
