554 
young shell. This fact is very interesting since here we also find a 
high degree of acceleration in other characters. Thus the dorsal 
furrow appears in the ananepionic substage at a considerable dis- 
tance from the gyroceran bend and continues after this, as shown in 
Fig. 20, along the dorsum and is continuous with that of the para- 
nepionic. 
The costations appear in the neanic stage. 
CYMATOCERAS DESLONCHAMPSIANUM. 
NavTILus DESLONCHAMPSIANUS, D’Orb. (Zerr. Jurass., Pl. xx). 
Loc., Rouen, France, Cretaceous. 
Bix bres. 22-07, 
This species, which is represented by several good specimens of 
the young, has very nearly the same ontogeny as Cymatoceras 
elegans, except, of course, in the specific characteristics and the 
position of the siphuncle. This last is propiodorsan in the meta- 
nepionic instead of being propioventran as in C. e/egans (2). The 
sutures of the early epembryonic stages differ from those figured by 
Branco for the same species, but this may be owing to the fact that 
we have reaJly observed different species. The dorsal furrow 
appears as in Cymatoceras elegans in the metanepionic at the second 
septum, as in Fig. 24, and is continued in the paranepionic sub- 
stage. 
CYMATOCERAS SIMPLEX (?). 
NAUTILUS SIMPLEX, Sow. (A@in. Conch., Pl. 122). 
Loc., England, Cretaceous. 
Bia. his. 28. 
This single specimen differs somewhat from the specimens of 
Cymatoceras deslonchampsianus and may be more distinct in the 
adult, but I do not feel sure of the fact that it is a different species. 
It has been figured in this connection because it shows that the 
dorsal furrow is present in this shell both in the metanepionic and 
paranepionic substages. 
CYMATOCERAS RADIATUM. 
NAUTILUS RADIATUS, Sow. (A@in. Conch., Pl. 356). 
NAUTILUS RADIATUS, D’Orb. (Zerr. Jurass., Pl. xiv). 
Loc., Rouen, Cretaceous. 
Pl. xii, Figs. 29 and 30, and Pl. xiii, Figs. 1 and 2. 
The ananeanic substage is shown in outline in centre of Fig. 30, 
