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Plate III. 



Figs. 1-7. Deroceras (Amm.) planicosta, Hyatt, Embryology Ceph. Bull. 

 Mus. Comp. Zoology, iii, No. 5, Pis. i and ii. 



Fig. 1, side view of nepionic and neanic stages, X 80 diameters. Fig. 2, sec- 

 tion of another specimen, X 21.5 diameters; B,protoconch. Fig. 3, centre of same, 

 enlarged to show the umbilical perforation (U) as it occurs in Ammonitinae and most 

 of the Goniatitinse. Fig. 4, protoconch and first volution with ananepionic first sep- 

 tum; x, probably sutures of the first septum on the dorsum seen through the whorl ; 

 X 80.* Fig. 5, side view of protoconch, ananepionic first septum 1 e, and meta- 

 nepionic septa, 2 e, 3 e; D, shell; B, naked cast of interior of protoconch; y, coni- 

 cal appendage of caecum seen through the whorl. Fig. 6, section of same speci- 

 men exposing interior of the protoconch (y), the conical caecal prolongation, and 

 the fundus of the caecum and the first two sepia, S, being the neck of the small 

 siphuncle at the third septum, which is broken off. Fig. 7, thin section of caecum 

 and part of conch with four septa, showing formation of caecum by the first septum 

 1 e, the composition of the caecal prolongation y, the neck of the caecum formed 

 by the second septum 2 e, the siphon begun by the third septum and continued 

 by the fourth, both of which have funnels directed apically as in Nautiloids ; S ; , 

 organic deposit in the interior; S", inner layer; S //; , wall of siphuncle; X 3 J 7 

 diameters. 



Fig. 8. Deroceras (s£goc.) planicosta, Branco, Paieontograp/iica,xxvii,T']. x, 

 showing protoconch from a different point of view and less magnified. Fig. 9, 

 same, with first to fourth sutures showing. 



Fig. 10. Pleuroceras (Amaltheus) spinatum, Branco (ibid.), PL xiii, enlarged, 

 showing the interior of the protoconch; the septa of first whorl are cut exposing 

 the caecum. The septa are all convex and strictly ammonitoidal except the 

 first, which is concave, as in Nautiloids and the adults of Mimoceras, Anar- 

 cestes and Agoniatites among Ammonoids of the Silurian period. 



Figs. 11 and 12. Crioceras Studeri, Branco (ibid.), PL xiii, enlarged, showing 

 the coiled young of this uncoiled degenerate form.f 



Figs. 13-18. Baculites compressus, Brown, Proc. Acad. Sci. Phila., i8o,i,p. 159; 

 1892, p. 136, PL ix. Fig. 13, enlarged young shell in the neanic stage, showing 

 the lines of growth, aperture and rostrum on the ventral side. Fig. 14, front view 

 of shell in the paranepionic substage; the siphuncle is not subventran. Fig. 15, 

 front view with the two metanepionic and four paranepionic sutures, those with a 

 siphonal lobe divided by a siphonal saddle being paranepionic in age. Figs. 16 

 and 17, front and side views, with restoration of the ananepionic substage. Fig. 

 18, side view of Fig. 15. 



Figs. 19-21. Apex from the front and side and sutures of Nautilus Clemen- 

 times, after Branco, op. cit., xxvii, PL ix. 



Fig. 22. Sutures of Nautilus deslongchampsianus, after Branco, (ibid.), 

 PL ix. 



* This figure has no number. 



f See also for similar forms PI. xi, Figs. 40, 41. 



