134 GENESIS OF THE ARIETIDjE. 



The forms figured by Wahner in his " Unteren Lias " 1 may be divided into 

 three subseries. It was not practicable to determine whether these series were 

 artificial or natural, though many figures of the young were given by Wahner. 



The first series can be distinguished by the finer pilie and somewhat com- 

 pressed whorls. They are as follows. Schlot. ccdenata, Wah., and angulata, in the 

 Planorbis bed. The following, though still discoidal, are slightly more involute 

 forms, if one can say this after comparison with Neumayr's figure of angulatum 

 from Pfonsjoch. 2 They are Schlot. montana, Wah., Plates XIX., XX., Donar, Plates 

 XIX., XXI., extranodosa, Plate XX., pachygaster, Plate XXI., and marmorea, Plate 

 XXII., and all occur in the Megastoma and Marmorea beds. 



The second or coarsely pilated series have more gibbous forms in the young 

 and much deeper channels, or, in other words, the pilse have more prominent ter- 

 minations on the abdomen. The discoidal forms are as follows. Schlot. ind., Plate 

 XVIII. Fig. 4, which has in an exaggerated condition the characteristics of the 

 subseries, and may be a pathological specimen, taurina, Plate XIX. Fig. 5, angu- 

 lata, var. ind., Plate XX. Fig. 5. All three of these were found in the Megastoma 

 and Marmorea beds, but were followed by two young forms occurring, according 

 to Wahner, in the Rotiformis beds. These are Schlot. scoMoptycha and posttaurina, 

 Plate XXIII., and appear to have been the young of species, which may have 

 been more involute in the adults. 



The third subseries has young with even stouter whorls than in the second 

 subseries, though not otherwise separable. Schlot. trapezoidale, the first species, 

 occurred, according to Wahner, in the Marmorea bed, and was succeeded by 

 ventricosa, Plate XXIII., and an undetermined form, Plate XXIII. Fig. 12, both 

 in the Rotiformis bed. 



Canavari in " Unteren Lias von Spezia " describes dwarfs or young of Schlot. 

 {^goc.) trapezoidale, Plate XVIII. Fig. 8, 9, and ventricosum, Plate XVIII. Fig. 10, 

 which seem to be identical with forms described by Wahner ; also Schlot. (JEgoc.) 

 catenatum, Fig. 1, comptum, Fig. 3-5, Collegnoi, Fig. 6, all of which are very closely 

 allied, and may be either young or dwarfs of Schlot. Charmassei, or the more invo- 

 lute varieties of Schlot. angulata. 



Second Subseries. 



The abdominal channel is narrower and deeper proportionally than in the 

 first subseries, and is a true furrow, in place of being a smooth zone or mere 

 depression formed between the interrupted pilae, as in Wrehneroceras and in the 

 first subseries of Schlotheimia. The shells known are finely pilated, and the 

 furrow is similar to what it is in the young of some species of the first subseries. 3 

 The species have been found only above the Bucklandi zone, and are all, so far 

 as known, dwarfs. 



1 Mojsis. et Neum.. Beitr., IV., 1886. 2 Abh. k. k. geol. Reichsans., VII., pi. ii. fig. 5. 



3 See Schlot. trapezoidale, Wah., Mojsis. et Neum., Beitr., IV. pi. xxiii. fig. 2 c, and others on the same 

 plate 



