FIFTH, OR AGASSICERAN BRANCH. 199 



gat-us, maintains the aspect of striaries until a late period of growth, and then 

 develops the keel and form of Scipionianus ; and there is also another fossil, which 

 is exactly similar to the later, but still immature, stages of Scipionianus. 



The keel may, perhaps, have a hollow above the siphon, such as Quenstedt 

 describes in his " Ammoniten des Schwabischen Jura," Plate XIV. Fig. 1, but 

 the inner or nacreous layer does not form a partition between the interior of the 

 shell and the interior of the keel, nor does the black layer occur above this par- 

 tition, as in Oxi/n. oxynotum and others, which have true hollow keels. In the 

 specimens examined, the keel was elevated, as in Quenstedt's figure, but the 

 siphon laid directly against the shell layers, which filled the interior of the keel, 

 and there was no black layer. 



Agassiceras nodosaries, Hyatt. 



Amm. nodosaries, Quenst., Der Jura, p. 78, pi. viii. fig. 8; Amm. Schwab- Jura, I. pi. xvii. fig. 1—3. 



Locality- ■ — Bempflingen. 



The specimen of this species in the Museum of Comparative Zoology is less 

 compressed than those figured by Quenstedt, but it shows that nodosaries is prob- 

 ably quite distinct from Scipionianus. The whorls are more compressed than in 

 the latter, but the tubercles and pilse are retained until a much later age. These 

 same distinctions are, of course, still more marked when the species is compared 

 with Scipionis. The exact horizon was not marked on our specimen. The 

 cast measured 160 mm., and the outer whorl 60 mm., the same whorl at the 

 beginning being somewhat less than 30 mm. ; the greatest transverse diameter 

 of the same was about 30 mm., and the least about 20 mm. Our specimen is, 

 therefore, a trifle larger than the inner whorl of the fragment figured by Quen- 

 stedt in "Ammoniten des Schwabischen Jura," Plate XVII. Fig. 1, at the point 

 marked "k." It is also of about the same diameter as his abdominal view of 

 the same whorl marked " q." The keel is also in the same condition, being 

 coated with matrix, the geniculae are bent and run nearly to the keel, there are 

 no channels, and on the younger part of this whorl the keel is well preserved and 

 prominent. Quenstedt's specimens were found in the Tuberculatus bed. It is 

 not unlikely that the compressed variety of Agas. Scipionianum described above 

 ought to be transferred to this species, but we have not been able to gather 

 sufficient evidence to settle this question. 



Agassiceras Scipionis, Hyatt. 



Plate IX. Fig. 12, 13. Suiimi. PI. XIII. Fig. 8. 



Amm. Scipionis, Reyne"s, Plates. 



Amm. Sclplonlanus ollfex, Qcenst., Amm. Schwab. Jura, pi. xvii. fig. 7-10 (not pi. xv.). 



Locality. — Semur. 



The shell of this species is smooth at an early age, and quite similar to the 

 old stages of Scipionianus in form and characteristics, but it is more involute, 

 Quenstedt's figures and descriptions of his Scipionianus olifex appear to apply to 



