﻿640 



siphuncle at about the same age. Fig. 16, another specimen from same locality, 

 showing the dorsal furrow in both metanepionic and paranepionic substages. 

 Both the last are enlarged 2 diameters. 



Figs. 17-19. Aturia Morissi Michellotti ; Baldasseres, Mus. Comp. Zoology; 

 Tertiary. Figs. 17 and 18, front and side views of the nepionic andneanic stages 

 enlarged 6 diameters. Fig. 19, nepionic stage, showing the umbilical perfora- 

 tion, seen from the exterior as a small black spot. 



Figs. 20-22. Aturia zizac, Sow.; Mus. Comp. Zoology; Tertiary. Figs. 20 

 and 21, side or front view of specimen from Dax, Bronn Coll., enlarged ten times, 

 showing apical character, siphuncle, first septum with deep lobes and caecum. 

 Fig. 22, side view of fragment of another specimen with umbilical perforation, 

 ananepionic substage in section and siphuncle. 



Plate XIV. 



Fig. 1. Eutrephoceras De Kayi. Reduced one-third. Two dorsal sutures, 

 showing the linguae form, minute, median saddles. 



Figs. 2-5. Barrandeoceras Stembergi (sp. Barrande) ; Schary Coll., Mus. 

 Comp. Zool. Reduced one-third. Fig. 2, from Lochkov, variety in which 

 whorls do not touch at all. Fig. 5, section of one, same locality, in which whorls 

 barely touch, showing that it has no contact furrow. Figs. 3 and 4, specimen in 

 which whorls touch in ephebic stage, but become free at the base of the living 

 chamber. This has throughout a flattened dorsum, but no contact furrow. The 

 appearance of a furrow in Fig. 4 is due to compression. These figures show also 

 the narrow dorsal lobes of the sutures. 



Figs. 6-12. Schroederoceras tubu latum, n. s. Reduced one-third. Coll. Mus. 

 Comp. Zool.; Loc, Brevig, Norway; Silurian. Figs. 6 and 7, nepionic stage. 

 Figs. 8-12, ana- and metaneanic substages. 



Figs. 13 and 14. Didymoceras nebrascense (sp. Meek). Reduced one-third. 

 Loc, near Buffalo Gap, So. Dakota; Coll., Yak University Museum; Cretaceous. 

 Views of the parephebic substage and gerontic stage. 



Figs. 15— 17. Emperoceras Beecheri. Reduced one-third. Loc, near Buffalo 

 Gap, So. Dakota; Yale University Museum; Cretaceous. Fig. 17 shows the 

 earlier stages with Hamites-like whorls from above. Fig. 16 shows the similar 

 apex of Fig. 15 corresponding in age to part of Fig. 17. Fig. 15, side view of 

 Fig. 16, giving the ephebic stage with its tubercles and bifurcated costae and the 

 parephebic substage with single costae and no tubercles. 



Figs. 18-21. Ptychoceras crassit?n ; Whitfield Coll., U. S. National Museum; 

 Loc, Boulder, Col. ; Cretaceous. Fig. 18, side view of ephebic and gerontic 

 limbs, with gerontic umbilical perforation, reduced one-third. Fig. 19, section of 

 same, natural size, showing the gerontic contact furrow. Fig. 20, view of dorsum 

 of gerontic limb, in and just orad of gerontic umbilical perforation, natural size ; 

 shows the gerontic dorsal furrow, with dorsal crests in lines of growth and one 

 costation and below the contact furrow. Fig. 21, section of the upper end of 

 Fig. 20, showing the gerontic dorsal furrow. 





