32 GENESIS OF THE AKIETID.E. 



examples; also the sutures, Plate VI. Fig. 9, of the young of S'cajJi. rcn/r/cosus, 

 Plate VI. Fig. 7 b, 8-8 b, of the same locality ; the pilse, the involution of the 

 whorls, and the sutures are also similar. It differs only in possessing the scaphi- 

 toid living chamber, which is well marked. This group of Scaphites are stouter, 

 and have different sutures from Placenticeras. 1 



In Europe Stephmwceras refraclum, the Annn. refractus of authors, is a true 

 Scaphites, but. no one thinks of calling it Scaphites, and it is usually referred 

 to the group of normal Ammonitina?, in common with several other distorted 

 forms. In an article on " Genetic Relations of Stephanoceras," 2 we discussed 

 the affinities of this and similar distorted forms, trying to show the former 

 existence of a general tendency to imitate the scaphitoid mode of growth in 

 Stephanoceras Gervilii, microstomum, and platysiomum. These species rebuilt a living 

 chamber at each arrest of growth, which was eccentric, having a flatter curva- 

 ture, and being smaller than the included whorl. This living chamber was also 

 resorbed at each period of renewed growth, as in Scaphites. 



The well known form Amm. vertebralis Sow., of the Upper Jura, was 

 described by Quenstedt as a diseased scaphitoid form, derived from Amm. 

 cordatum, and this conclusion has also been confirmed by my own observations. 

 Stephanoceras bulMum ' ! has a shell which is precisely like typical Scaphites in 

 the form and aspect of the last whorl, but does not depart from the spiral as 

 in Scaphites. It is. in other words, intermediate between Scaphites and the 

 normal closely coiled Ammonitinre of the Stephanoceran group. The Amm. 

 microstomas impresses of the Upper Jura is figured by Quenstedt as a form of 

 Steph. mwrostomun, to which it has a close similarity, although smaller, and the 

 author concentrates his knowledge of the relation of these forms in one sen- 

 tence, "Scaphites sind haufig nur kranke Ammoniten," — Scaphites are often 

 only diseased Ammonites. This statement, which was also Von Buch's opinion, 

 requires a qualification, since they are not simply sick or diseased Ammonoids, 

 occurring sporadically like occasional distortions, but races or stocks with cata- 

 plastic tendencies inherited and increasing in successive generations. 



The distribution, affinities, and cataplastic nature of these forms indicate 

 local origin, but during the cretaceous period unfavorable conditions prevailed 

 so generally that series of them were produced independently, and apparently 

 simultaneously, in many localities in Europe and in this country. Thus, equiv- 

 alent series of nostologic forms, like Scaphites, Ancyloceras, and Baculites, arose 

 in groups of species, which were not genetically connected with one another, but 

 more or less closely with widely separated and distinct genera of the progressive 

 Ammonitinai and Lvtoceratinge. 4 



1 These remarks, however, are considered to be simply suggestions, which the author purposes to follow 

 out and publish with proper details. 



■ Proc. Bost. Soc. Nat. Hist., XVIII., 1S76, pp. 370-:M. 



3 Die Ceph., p. 61. 



1 Zittel, in his admirable " Handbuch der Paleontologie," I. pp. 440-4-16, adopts Xeurnayr's opinion as 

 to the connection of the typical cretaceous genera of Hamites, etc. with the Lytoceratinse, founding his belief 

 in their genetic connection upon the sutures and smooth shell. On pages 481, 4SJ. he confirms Neumayr's 

 and Uhlig's opinion of the variety of genera from which the more ornamented shells of Ancyloceras, C'rio- 

 ceras, etc. had been derived. 



