32 GENESIS OF THE ARIETIDA. 
examples; also the sutures, Plate VI. Fig. 9, of the young of Scaph. ventricosus, 
Plate VI. Fig. 7 b, 8-8 b, of the same locality; the pile, 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.' 
In Europe Stephanoceras refractum, the Amm. 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 Ammonitinz, in common with several other distorted 
forms. In an article on “Genetic Relations of Stephanoceras,’* 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 Gervili’, microstomum, and platystomum. 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 Arun. 
cordatum, and this conclusion has also been confirmed by my own observations. 
Slephanoceras bullatum® 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 Ammonitine of the Stephanoceran group. The Ami, 
microstomus impresse of the Upper Jura is figured by Quenstedt as a form of 
Steph. microstomun, 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 
Ammonitine and Lytoceratine.* 
1 These remarks, however, are considered to be simply suggestions, which the author purposes to follow 
out and publish with proper details. 
2 Proe. Bost. Soc. Nat. Hist., XVIII., 1876, pp. 870-384. 
8 Die Ceph., p. 61. 
4 Zittel, in his admirable ‘‘ Handbuch der Paleontologie,”’ I. pp. 440-446, adopts Neumayr’s opinion as 
to the connection of the typical cretaceous genera of Hamites, etc. with the Lytoceratinz, founding his belief 
in their genetic connection upon the sutures and smooth shell. On pages 481, 482, he confirms Neumayr’s 
and Uhlig’s opinion of the variety of genera from which the more ornamented shells of Ancyloceras, Crio- 
ceras, etc. had been derived. 
