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Plate VIII. 



Figs. 1-8.* Remeleceras impressum; no locality: Coll. Mus. Comp. Zoology. 

 Natural size. Fig. I, side view showing sutures and annular muscle in base of 

 living chamber. Fig. 2, ventral side of fragment of same specimen. Fig. 3, dor- 

 sal side of same fragment with impressions of annular muscles on cast. Fig. 4, 

 section of end of living chamber showing the decrease of the impressed zone in 

 the anagerontic substage. Fig. 5, dorsal view of the second and younger frag- 

 ment of same. Fig. 6, section of older end of same showing depth of impressed 

 zone in the ephebic stage. Fig. 7, still younger fragment of same, showing the 

 dorsal sutures of a late neanic or anephebic substage. Fig. 8, section. 



Figs. 9-13. Hercoceras minim, Barrande. Figs. 9-12, slightly enlarged, 

 Koneprusy. Fig. 13, natural size, Hlubocerpy, Mus. of Comp. Zoology, Schary 

 Coll. Figs. 9 and 10, side view and front of the ananeanic substage showing first 

 beginning of contact furrow and the trochoceran form of the young which is more 

 marked than in the adult. Figs. 1 1 and 12, side view and front of paranepionic 

 substage of the same specimen showing the absence of the dorsal furrow just be- 

 fore the apex is reached. 



Figs. 14 and 15. Hercoceras irregularis (sp. Barrande), Hyatt; Loc, Bohemia; 

 Mus. Comp. Zo5l. Fig. 14, side view of meta- and paranepionic volution, show- 

 ing the peculiar costae without longitudinal ridges of this genus. Fig. 15 shows 

 the form in section of the meta- and paranepionic whorl and the absence of the 

 contact furrow in correlation with the rounded form of whorl. The caecum is not 

 correct; this organ is large and ventrocentran in this specimen. 



Figs. 16-20. Anomaloceras onomalum (sp. Barrande), Hyatt; Mus, Comp. 

 Zoology, Schary Coll. Slightly enlarged. Fig. 16, section passing through umbil- 

 ical perforation which is filled with a peculiar dense shell-like deposit, not found 

 so far in other forms, and also cutting the meta- and paranepionic substages. The 

 neanic stage with a deep impressed zone and the two sections of the outer whorl 

 which are in the ephebic stage. The siphuncle appears to be nearer the centre 

 in the metanepionic substage in this and in Fig. 17 than in the later stages. 

 There is a dorsal furrow at the usual place beginning beyond the gyroceran curve 

 in the paranepionic substage in correlation with the nephritic outline of'this sub- 

 stage. Fig. 17, view of a section of the metanepionic and paranepionic substages 

 of same cutting deeper into the umbilical perforation which is becoming nar- 

 rower. Fig. 18, a still deeper cut which has passed through the apex of the 

 conch and shows the first contact of the whorls. Fig. 19 shows the beginning 

 of the contact zone, the paranepionic section having passed into the ananeanic and 

 below the rounded ananepionic has replaced the metanepionic volution. Fig. 20, a 

 still deeper cut, showing the shell of the ananepionic substage becoming broader 

 through the approach of the section to the exterior of the ananepionic apex. A 

 shade farther and the ananeanic and metaneanic sections would blend into one 

 long figure and the ananepionic would disappear. 



Figs. 21-23. Discoceras Graftonense (sp. Meek and Worth en), Hyatt; Loc, 

 Waukesha, Wis., Niagara Group; Mus. Comp. Zoology, Day Coll. Natural size. 



* Fig. 1 has no number on the plate. 



