636 
dorsal furrow in paranepionic substage. The sutures, of course, belong to the 
neanicstage. Fig. 25 shows the minute umbilical perforation and the close coiling 
of the whorl. Figs. 26 and 27, apex of same, enlarged 3 diameters and giving 
ornamentation of shell and cicatrix. ‘The dorsal furrow begins at the first or 
gyroceran bend in the paranepionic substage. 
Figs. 28-31. Cenoceras lineatum (?), Oolite (Naut.) aratus of Quenstedt’s 
Coll., Tiibingen, from sketches in my notes, showing the nepionic stage with 
dorsal furrow as in “veatus. 
Figs. 32-35. Cenoceras (Naut.) aratus, Saemann’s original specimen; Mus. 
Comp. Zodlogy; Middle Lias; Suabia. Figs. 32 and 33, enlarged 2 diam- 
eters, showing markings on the cast, form of nepionic stage, large umbilical per- 
foration and sutures. The shell probably had longitudinal ridges and bands of 
growth on the dorsum as well as on the venter. Figs. 34 and 35, copied from 
Embryology Ceph., Hyatt, Pl. iv, much enlarged and corrected to show ana- and 
metanepionic substages and annular lobe, which begins in the third suture, The 
dorsal furrow begins between the third and fourth sutures, the last being the 
oldest in Fig. 35. The curvature is uniform, gradual, and there is apparently no 
mechanical cause for its early appearance in this shell. 
Figs. 36-39. Cenoceras (Naut.) granulosus (sp. D’Orb.), Chatillon; Coll. 
Boucault, Oxfordian; Coll. Mus. Comp. Zod]. Slightly enlarged. Figs. 36 and 
37, showing extraordinary quick growth of the dorso-ventral diameters in ana- 
and metanepionic substages and beginning of paranepionic with dorsal furrow 
in what is probably the fourth septum. Figs. 38 and 39, similar views of another 
older specimen in paranepionic substage. See also Pl. xii, Fig. 31. 
Fig. 40. Crioceras (?) Studerd, Ooster, after Barrande, Callovian, much en- 
larged, to show the close-coiled first volution. 
Fig. 41. Ancyloceras (?) calloviense, after Barrande, Callovian, much enlarged, 
to show the close-coiled young. 
