12-4 GENESIS OF THE ARIETIDjE. 



planorbe. The saddles sometimes have entire margins, as in some Ceratitinae of 

 the Trias. Neumayr's Hagenowi, in his " Unterster Lias Nordalpen," * is not a 

 true Hagenowi, if the sutures are correctly drawn. Such facts and the remark 

 of Wahner quoted above (page 113) show that Hagenowi is probably a dwarfed 

 deformation of Psil. planorbe, which is likely to occur in any locality, and has an 

 independent existence as a race or species only in certain basins where it is 

 abundant. It seems to indicate, wherever it appears, that Psil. planorbe has there 

 been subject to unfavorable conditions. 



Neumayr in the work above quoted, Plate IV. Fig. 1, gives a Psil. {JEgoc.) 

 Naumanni, a good-sized species with numerous folds, compressed slightly conver- 

 gent sides, and a rounded smooth abdomen, exactly the form and characters of his 

 Hagenowi, except that it is more decidedly plicated. The smaller Psil. (^Egoc.) 

 erebrispirale, Ibid., Plate V. Fig. 4, is probably the young of this shell. The sutures 

 have complicated margins, as in other shells of this province, and are not similar 

 •to those of Hagenom. We place it here until its exact affinities can be settled 

 by the study of a series, or of the young. 



JEgoceras Struckmanni* Ibid., Plate VI. Fig. 5, as remarked by this distinguished 

 authority, is a unique survival of triassic forms. It resembles the flat-sided 

 whorls in Tirolites, and even certain earlier forms, like Popanoceras. It may be 

 provisionally associated with this series until the sutures are known, since the 

 shell is smooth, and similar to that of Psil. planorbe. This series should be care- 

 fully studied with ample materials. It may be that confusion exists between 

 some forms now supposed to be true Psii. Hagenom and some triassic forms 

 still surviving in the Lias. Canavari, in his " Fauna del Lias Inferiore di Spe- 

 zia," 188S, Plate VII., has figured a series of what appear to be true Tropites. 

 These are very close congeneric forms of this triassic genus, and in our opinion 

 should be referred to Tropites itself. 3 This gives greater force to the suggestion 

 made above. 



Canavari, in his " Fauna des unteren Lias von Spezia," gives some interesting 

 forms of this genus. Psil. (JEgoc), Plate XIX. Fig. 2, 4, 5, is a plicated form 

 similar to pleuronolum. Psil. pleuronolum, Plate XIX. Fig. 3, may possibly be the 

 same as Psil. calcimontanum, as stated by Wahner, but it is a dwarf, like most of 

 the species from this locality. Psil. {JEgoc. .) Portisi, Plate XIX. Fig. 6, appears 

 to bear a similar relation to Psil. mesogenos. Wahner, however, considers it iden- 

 tical with the young of his Psil. Kammerkarense? 



1 Abhandl. geol. Reiehsans. AVien, VIT. pi. ii 



2 Winner's Psil Struckmanni, Unt. Lias, iUojsis. et Neum., Beitr., IV. p. 196. 



3 The survival of characteristic triassic forms in the Jura shows that the connections between these 

 two systems are closer than has been supposed, and gives support to opinions advocated in the chapter on 

 Geological and Faunal Relations, and adds another group to the three already noted, Psiloceras, Lytoceras, 

 and Phylloceras. These facts demonstrate that no insuperable barrier arrested the migration of forms and 

 the continuity of the faunas in time. See remarks on Tropites in note to page 151. 



4 Paleontogr., XXIX., and also Mem. del. Car. Geol. d' Italia, III., 1888. 



