SECOND, OR SCHLOTHEIMIAN BRANCH. 



127 



and in Volume II. he figures Week, extracostatum, Plates XIV., XVI., and Pamneri, 

 Plates XV., XXI. The figure of extracostatum shows an old whorl which is acute, 

 but not involute. Among discoidal shells, Week, circacostatum, Plates XV., XVI., 

 curviornahm, Plate XVI., and haploptychum, Plate XVII., show that the whorls of 

 their earlier nealogic and adult stages are without channels. Wceh. anisophyllum, 

 Plate XIX. Fig. 1 a, shows a very old stage with subacute trigonal whorl, and 

 pilse replaced by folds. Wceh. megastoma, Plate XVIII. Fig. 2, 3, shows ear- 

 lier nealogic stages with pilse continuous across the abdomen in the adult and 

 senile stages. Wceh. euptychum, Plates XVIIL, XX., stenoptychum, Plate XX., 

 latimontanum, Plate XX., and diphptychum, Plate XXI., also belong to this ge- 

 nus. The last two are senile specimens, with subacute outer whorls, and all 

 the above are discoidal shells exhibiting transitions from Psiloceras to Schlo- 

 theimia. 



There are, however, involute forms in this series also figured by Wahner in the 

 same work, but in Volume IV. These are Wceh. Gkddoni, Plate XXVI. Fig. 3 a, b 

 (not Fig. 7), and Wceh. Emmrichi, Plate XXVI. 1 We 

 doubt whether either of these involute forms' can 

 be regarded as transitional to Schlotheimia, as sup- 

 posed by Wahner. 



The results of our work upon the nealogic 

 stages and their meaning in Schlot. catenata, and all 

 other species, show that series arose only from dis- 

 coidal shells, and probably never originated from 

 the compressed and involute forms. These are 

 themselves invariably discoidal and less compressed 

 in their own young, showing them in every case figures .2 



to have been derived from shells having depressed abdomens and discoidal 

 whorls. 



Canavari, in his " Unteren Lias von Spezia," 3 describes and figures dwarfs or 

 the young of Wceh. {JEgoc.) Emmrichi under the name of Guidoni. Wahner thinks 

 that Canavari's forms (Plate XVIII. Fig. 14, 15) are referable to his Guidoni, and 

 Fig. 16 to be identical with his Emmrichi. The last is to us a very remarkable 

 form, since it possesses continuous lateral and abdominal constrictions. 



20 21 22 



Fig. 20-22. — Views from in front, 

 side, and abdomen, of tlie young of Wceh. 

 Emmrichi, after Wahner, showing the 

 involution of this species. The charac- 

 teristic piUe and channelless abdomen of 

 this genus are also noticeable in these 



SCHLOTHEIMIA. 



The form varies in this genus from discoidal to involute, but the umbilici are 

 never entirely covered in. The whorls are usually flattened more or less on the 

 sides, and the abdomen depressed. In the nealogic stages this form is common, 



' 1 We have given outline figures of Wceh. curciornalum, Summ. PI. xi. fig. 7, haploptychum, fig. 8, toxo- 

 phorum, fig. 9, and Emmrichi, fig. 10. 



2 This figure, according to Wahner, is poorly drawn, the last volution too narrow, the umbilicus too 

 open. It, however, exhibits the general aspect of involute forms in this series, and we have retained it 

 with that purpose in view. 



8 Paleontogr., XXIX., and Mem. del. Carta Geol. d' Italia, III., 1888. 



