24 GENESIS OF THE ARIETID. 
normal forms of that genus. Wiirtenberger has come to similar conclusions, and 
has traced a large part of the same genera back to the same origin in the work 
quoted above. We differ in details, and in the way in which we treat the stem 
of stock forms, but these differences will probably disappear after further re- 
searches have been made. His book is full of the evidences of careful work, and 
we do not feel disposed to offer any criticisms until there is an opportunity to 
publish our own observations in detail. The young forms of the Spinifera in the 
later nepionic stage, have a very close resemblance to the young of Tropites 
before the keel appears, and also an obvious reference to Tirolites of the Trias, 
and to the more remote and possible ancestor, Glyph. diadema, in the Carboniferous. 
Per. Defranci is the radical of all of the species of the large genus Peri- 
sphinctes, and has no tubercles in the adult, but in the young there is a prolonged 
stage like the adult of discoidal coeloceran species, and in still younger stages a 
pettos-like stage. This genus embraces a very large number of species which 
have been traced out by Wiirtenberger, and referred by him to a species closely 
allied to the one quoted above in the Lower Odlite. The absence of tubercles, 
and the rounded form of the whorl in this group, and the frequent absence 
of the trapezoidal form and tubercles even in the early stages of many species, 
show that it is distinct from the Spinifera. We propose to designate it by the 
term Plicatifera. 
The tertiary radicals of the keeled groups, the Carinifera, as we propose to 
call them, have also close structural relations, but are modifications of what we 
have called the quadragonal form. Nevertheless, in the young and the adults 
there is a tendency to reproduce the tertiary radical of the Spinifera. This 
is to be seen in Wihner’s figures of Caloceras (Arietites) Coregonense, and that 
keen observer describes the resemblance of the young just before the keel ap- 
pears to Cal. Pettos of the Middle Lias. Similar facts can be noted in the young 
of other forms of the Arietidse, but the keeled stage acquires prepotency in the 
Arietide. Their quadragonal, keeled, and channelled forms began in Caloceras, 
and from this genus sprang the similar tertiary radicals of the later Jura. The 
adical stock is continued by such species, as follows: Amaltheus Hawskerense, 
Phymatoceras enervatum, EHildoceras Walcott, and Harpoceras Sowerbyi, which last 
has a thodified quadragonal form until a late stage of growth in some varieties, 
Oppelia hecticus also has in some varieties a quadragonal form until a late stage, 
though not so discoidal as most of the preceding. In the Cretaceous, there 
is Schlanbachia tricarinatus and Westphalicus, which are true stock forms of the 
Cariniferae.” 
Haploceras, Desmoceras, Silesites, Pictetia, and the like, have tertiary radicals 
similar to the typical forms of Lytoceras, and belong therefore to the Lytoceratine. 
1 Mojsis. et Neum., Beitr., VI., 1888, pl xxii. 
2 If should be noticed in this connection that the characteristics of the so-called pettos-like young of the 
earlier occurring species of the Carinifera are favorable to Mojsisovics’s view that the Arietide sprang from 
Halorites. This genus is closely related to Tropites, and the form and sutures of the young of several 
species in the Arietide certainly show affinities for Tropites. On the other hand, as we have maintained 
above, the affinities and gradations of all the species of the Arietide lead us back into Psiloceras, and the 
alliance of that genus with Gymnites seems to be closer than with any other in the Trias, 
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