24 GENESIS OF THE ARIETIDJE. 



normal forms of that genus. Wurtenberger 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 feef 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 nrepionic 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, diudema, in the Carboniferous. 



Per. Dcfranci 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 Wurtenberger, and referred by him to a species closely 

 allied to the one quoted above in the Lower Oolite. 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 Wahner's figures of Calocems (Arictites) Coregonense} and that 

 keen observer describes the resemblance of the young just before the keel ap- 

 pears to Gael. 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 

 ArietidtB. Their quadragonal, keeled, and channelled forms began in Caloceras, 

 and from this genus sprang the similar tertiary radicals of the later Jura. The 

 radical stock is continued by such species, as follows : Amaltheus Hawslcerense, 

 Phymatoceras enervaiam, Hildoceras Wcdcoti, and Harpoceras Soiverhyi, which last 

 has a modified quadragonal form until a late stage of growth in some varieties. 

 Oppelia heciicus 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 Schloenbachia tricarinatus and Westphalicus, which are true stock forms of the 

 Cariniferse. 2 



Haploceras, Desmoceras, Silesites, Pictetia, and the like, have tertiary radicals 

 similar to the typical forms of Lytoceras, and belong therefore to the Lytoceratinas. 



1 Mojsis. et Neum., Beitr., VI., 1888, pi. xxii. 



2 It 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 Arietidfe sprang from 

 Halorites. This genus is closely related to Tropites, and the form and sutures of the young of several 

 species in the Arietidaj certainly show affinities for Tropites. On the other hand, as we have maintained 

 above, the affinities and gradations of all the species of the Arietidag lead us back into Psiloceras, and the 

 alliance of that genus with Gymnites seems to be closer than with any other in the Trias. 



