ORIGIN AND CHARACTERISTICS OF SUBORDERS. 5 
saddles are phylliform. The young of Monophyllites Suessi, Moj.,' of the Trias, 
has sutures similar to the adults of Popanoceras antiquum® and Kingianum of the 
Dyas,’ which are true Goniatitine. The sutures of Popanoceras are in their 
turn transitional between Monophyllites and the more normal Goniatitine: of 
the genus Prolecanites. 
Triassic Ammonoidea have shallow ventral lobes and very prominent broad 
siphonal saddles, thus giving the first lateral saddles the aspect of being ad- 
juncts of the siphonal saddle. . In consequence of the more direct descent 
of Lytoceratinz of the Jura from primitive forms, their sutures persist in 
retaining triassic outlines, having usually short abdominal lobes, large siphonal 
saddles, with the superior laterals apparently set upon their sides, the larger 
lobes expanded and profusely branching at the top, the saddles expanded 
and profusely branching at the base, the auxiliary lobes and saddles more 
numerous and more nearly equal to the larger lobes and saddles than in 
Ammonitine. Neumayer has demonstrated trumpet-like apertures in Lyt. am- 
mane* The frilled and elevated ridges in shells of many forms indicate that 
these are perhaps not uncommon in this group.’ 
The normal forms of the Ammonitinz, the Arietidee of the Lower Lias, 
can be united to the genus Gymnites through Psiloceras. Gymnites can be 
traced back to the Goniatitinee through Arcestes of the Trias and Cyclolobus 
of the Dyas. The Ammonitine do not, therefore, come directly from the 
Goniatitine, as do the Lytoceratine, but are probably direct offshoots of the 
lower Arcestine. The Ammonitine include not only the typical jurassic and 
cretaceous forms, but also the allied radical genera Schlotheimia and Psilo- 
ceras of the Lias, and Gymnites and Ptychites of the Trias.° 
In Gymnites of the Trias, the primary radical is exchanged for the more 
compressed discoidal secondary radical, but still smooth shell, which is also 
characteristic of Psiloceras of the Lias. The sutures are correlatively modified, 
and begin to assume the aspect and proportions of the true Ammonitine. The 
siphonal saddle is more prominent, but still retains in many species the pointed 
aspect derived from the Goniatitine. The narrow first lateral saddles are apt to 
appear like adjuncts of the siphonal saddle, owing to the great size and breadth 
1 Mediterr. Triasprov., pl. Ixxix. fig. 4 a-e. 
2 Arcestes antiquus, Waagen, Salt Range, Pal. Ind., ser. 13, I. i, pl. i. fig. 10. 
8 Russia and Ural, M. V. K., II. pl. xxvii. fig. 5. 
4 Mojsis. et Neum., Beitr., II., 1883, 1884, pl. xx. 
5 Schlonbach, Paleontogr., XIII. p. 169, pl. xxvii. fig. 3, describes Amm. hircicornis, one of the 
Lytoceratine, having a series of prominent flaring ridges indicating permanent apertures of similar 
form. The slight, blunt rostrum is a notable characteristic of these apertures. Unfortunately, very 
few have been preserved, possibly owing to the fact that they were in most species, as in the two 
mentioned, thin flaring ridges, easily destroyed. We can only suggest, therefore, that this form of 
rostrum might have been peculiar to this suborder, 
6 In “Genera of Fossil Cephalopods,” in 1883, we expressed this opinion as follows: ‘‘This genus 
(Cyclolobus) is very important, since it enables us to show the gradations by which the Prolecanitide 
approximate to Arcestes, Ptychites, and Monophyllites.’? Mojsisovics, with new materials from Spitz- 
bergen, has lately demonstrated the correctness of this opinion in part, and gives conclusive evidence 
of the probable derivation of Arcestes and Ptychites from Popanoceras, Arkt. Trias Fauna, Mem. Akad. 
St. Petersb., XX XIII. No. 6, p. 66, pl. xv. 
