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Plate IV. 



Fig. I Baciilites compressus, enlarged sutures after Brown, see PI. iii.* 



Fig. 2. Deroceras (Aegoceras) planicosta, enlarged sutures after Branco, 

 Paleontographica, xxvi, PI. x. These show the ananepionic suture I, the metane- 

 pionic or goniatitic sutures 2-4, and the paranepionic with divided siphonal lobe 

 at the diameter of 1 ram. and 2 mm., and the next septum, the 7, here given, is 

 transitional to the first neanic septum, the 8 of this series, which shows the begin- 

 ning of ammonitic digitations in saddles and lobes and a divided dorsal lobe. 

 By comparing this with the sutures of PI. ii, Fig, 16, Anarce*tes lateseptatus, and 

 Gephuroceras serratum, PL ii, Fig. 17, it will be seen that the ephebic ventral 

 lobes and smooth sutures of the Goniatitinae, represented in Gephuroceras, are 

 limited to the paranepionic in Deroceras. The goniatitic ventral lobe in other 

 words is replaced in the ananeanic of Deroceras, representing the Ammonitinse, 

 by the digitate lobes and saddles of that suborder. 



Fig. 3. Vermiceras (Arietites~) spiratissimum, enlarged sutures, after Branco, 

 {ibid.), PI. ix, showing also acceleration of development through the replacement 

 of the ephebic characters of the Goniatitinae by those of the Ammonitinae in the 

 ananeanic substage. 



Fig. 4— 11. Tarphyceras Champlainense, (sp. Whitfield), Hyatt; Loc, Fort 

 Cassin; U. S. N. Mus., Walcott Coll. Fig. 4, side view slightly enlarged, show- 

 ing involution and small unbilical perforation ; the crack indicates the direction 

 of the section given in Fig. 5. Fig. 6 gives general section and the centre is of 

 about the same age as Fig. 6. Fig. 7 is younger and shows beginning of the 

 dorsal furrow narrower and deeper than in Fig. 6. Fig. 5 shows that it is 

 probably due to the mechanical effects of the sudden bending shown in Fig. 7. 

 Fig. 8, ideal section showing location of sections Figs. 6 and 7. Fig. 9, section of 

 another specimen, natural size, showing a younger stage at the centre. Fig. 10, 

 side view of same specimen. Fig. 11, enlarged section of metanepionic centre of 

 Fig. 9, showing outline like that of Nautilus pompilius at the same age. 



Fig. 12— 16. Tarphyceras prematurum, Hyatt, Quebec Group; Loc, Port au 

 Port, Newfoundland. Fig. 12, side view of fragmentary specimen, natural size, 

 giving part of living chamber. Fig. 13, front view of same. Figs. 14 and 15, front 

 and side view of nepionic and part of neanic stage slightly enlarged ; Fig. 16, front 

 view of nepionic whorl of same (X 2 ) showing a dorsal furrow and the abrupt 

 bending of the whorl. The narrowness of the umbilical shoulders is not natural, 

 being probably in part due to the obliquity of the septum and partly to erosion of 

 the outline at this point. 



Figs. 17-22. Tarphyceras Aucoini, Hyatt, Quebec Group; Loc, Port au Port, 

 Newfoundland. Fig. 17, side view, natural size, of ephebic stage; Fig. 18, part 

 of neanic whorl to show sutures. Fig. 19, section of ephebic whorls, natural size, 

 of another specimen. Fig. 20, section, natural size, of another specimen, the upper 

 whorls a little depressed by pressure; Fig. 21, the nepionic stage enlarged (four 

 diameters) to show more accurate outline and the dorsal furrow and sudden bend- 

 ing of whorl and narrow umbilical perforation. Fig. 22, side view of same. The 

 apex in all of these specimens was too much eroded to show the cicatrix. 



•This figure is not numbered. 



