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dorsal furrow in paranepionic substage. The sutures, of course, belong to the 

 neanic stage. 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. 2S-31. Cenoceras lineattim (?), Oolite (Naut.) aratus of Quenstedt's 

 Coll., Tubingen, from sketches in my notes, showing the nepionic stage with 

 dorsal furrow as in lineatus. 



Figs. 32-35. Cenoceras [TVaut.) aratus, Saemann's original specimen ; Mus. 

 Comp. Zoology; 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 Cefik., 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. Zool. 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 (?) Studeri, 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. 



