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Plate XI. 



Figs. 1-3. Peripetoceras {Naut.) Frieslebeni (sp. Geinitz) ; Loc, Tunstall 

 Hill, England; Mus. Comp. Zool.; Dyas. Natural size. Fig. I shows the 

 section through the apex of the conch, the ananeanic volution below and a 

 later age of the neanic stage above. Fig. 2, the cut has passed through, the um- 

 bilical perforation, the metanepionic above this and the paranepionic below ; 

 above the metanepionic is the paraneanic or anephebic substage. Fig. 3, the 

 cut has approached the farther side of the umbilical perforation and shows an 

 older age of the metanepionic and a younger age of the paranepionic with a deeper 

 and better defined dorsal furrow than in Fig. 2. 



Figs. 4-8. Syringoceras {Naut.) granulosostriatus, after Mojsisovic's Medit. 

 Triaspr., PI. lxxxii, Figs. 7 and 9, Trias. Figs. 4 and 5, nepionic stage enlarged. 

 Fig. 8, more enlarged view of apex, with a cicatrix. Figs. 6 and 7, paranepionic 

 and ananeanic substage with longitudinal striations and beginning of impressed 

 zone after contact. 



Figs. 9-12. Syringoceras {Naut.) Linearis, after Laube; Fauna St. Cassian 

 De?iksch. Akad. Wien, 1869, PI. xxxvi, Trias. Fig. 12, natural size. Figs. 9-11, 

 enlarged. Fig. 10, to show more accurately shape of apex. All show nepionic 

 stage and development same as in granulosostriatus. 



Figs. 13 and 14. Digonioceras {Naut.) excavatum, after D'Orbigny, Terr. 

 Jurass., PI. xxx, Lias. These show the nepionic stage with an impressed zone 

 existing before contact, also the annular lobe. 



Figs. 15 and 16. Cenoceras {Naut.) intermedium (sp. Sow.), Balingen, De 

 Koninck Coll. Mus. Comp. Zool. ; Middle Lias. Slightly enlarged. These show the 

 large umbilical perforation and sutures, the paranepionic and ananeanic substages. 

 The dorsal furrow is present only in the paranepionic substage and the beginning 

 of the contact furrow is shown also in the shaded area on the dorsum of Fig. 16. 



Figs. 17 and 18. Cenoceras {Naut.) intermedins (?) (sp. Sow.), after Bar- 

 rande and Hyatt, Syst. Si/., PI. cccclxxxix, Fig. 7; D'Orbigny Coll. Jarden des 

 Plantes ; Middle Lias. These show the ana- and metanepionic substages with 

 cicatrix and sutures, but no impressed zone. 



Figs. 19-21. Digonioceras sp. ? (similar to excavatus) , Balingen ; De Koninck 

 Coll., Mus. Comp. Zool. ; Middle Lias. Natural size. Fig. 19 shows sutures, 

 etc., of paranepionic substage. Fig. 20 gives outline of same from dorsum with 

 the dorsal furrow in the paranepionic, the upper outline of this figure is incorrect 

 since the dorsal furrow begins immediately below this. Fig. 21 gives this out- 

 line correctly, it being the last of the ananepionic substage at the second suture ; 

 in Fig. 21, the venter is placed uppermost for comparison' with Fig. 20. 



Figs. 22-27. Cenoceras lineatum (sp. Sow.), Bayeux; Coll. Duval, Mus. 

 Comp. Zoology ; Inferior Ool. Fig. 22, natural size, showing umbilical per- 

 foration, metanepionic substage below perforation and paranepionic above this, 

 the neanic stage being below the metanepionic volution. The dorsal furrow 

 is well developed in the paranepionic substage. Fig. 23, the reverse of the two 

 upper sections of Fig. 22. 



Figs. 24 and 25, views of another specimen, showing the nepionic stage, en- 

 larged 3 diameters, showing the position of the siphuncle ventrad of centre and 



