570 MR. L. F. SPATH ON [Dec. I913, 



Genus Perisphinctes Waag. em. Siem, 



Perisphinctes (Groessoevria) cf. regalmtcensis (Gemmellaro). 

 (PI. LIII, figs. 3 a & 3 b.) 



1875. Ammonites reqalmicensis Gemmellaro, 'Faune Giur. & Liass. della 

 Sicilia ' p. 119 & pi. xiv, fig. 3. 



[1867. Ammonites birmensdorfensis Moasch, 'Aarg. Jura' Beitr. z. Geol. Karte 

 der Schweiz, No. 4, p. 291 & pi. i, fig. 3.f 



1898. J. von Siemiradzki, ' Monogr. Beschreib. der Ammonitengattung Peri- 

 sphinctes ' Palaaontographica, vol. xlv, p. 87 & fig. 4. 



The outer whorl of my specimen is somewhat worn, so exact 

 measurements cannot be made ; but the umbilicus amounts to 

 probably 55 per cent, of the diameter, and this exceedingly slow 

 character of the coiling, together with the obliqueness of the con- 

 strictions, forms the most noticeable feature of my specimen. It 

 resembles in this respect, as well as in its state of preservation and 

 size, the ammonite figured by Gemmellaro ; but, according to 

 Siemiradzki, P. regalmicensis has flattened sides, whereas the 

 rounded walls of my specimen remind one of P. birmensdorfensis 

 Moesch, although the costation of the latter form is finer. This 

 has also a larger umbilicus (57 per cent.) than P. reyalmicensis 

 Gemm. ; but, on the whole, I am inclined to associate my specimen 

 with the Sicilian form, as the figure given by Moesch also shews 

 the last constriction to be almost radial instead of being still 

 strongly prorsoradiate. 



In P. navillei Favre the obliquity of the costse, and especially 

 of the constrictions, is a still less noticeable feature. 



The ammonite is undoubtedly of Argovian age. 



Perisphinctes (Grossoevria) cf. navieeei Favre. 



1875. E. Favre, 'Descr. des Foss. du Terrain Jurass. de la Montagne des 

 Voirons ' Mem. Soc. Pal. Suisse, vol. ii, p. 34 & pi. iv, fig. 1. 



The identification of this specimen is difficult, owing to its bad 

 state of preservation ; but it seems to be closely comparable with 

 Favre's form from the Birmensdorf Beds of Voirons. 



At a diameter of 60 millimetres the umbilicus measures 49 per 

 cent., and there are about fifty-five costae slightly prorsoradiate, 

 but becoming worn near the venter, so that my specimen might 

 even be a Simoceras, two forms of this genus (randenense and 

 doublieri) being very similar. 



Perisphinctes birmensdorfensis (Moesch) has a larger umbilicus 

 (57 per cent.) and a circular whorl-section, as well as closer 

 costation, which latter also distinguishes P. regcdmicensis Gemm. 

 from my specimen. 



The ammonites which A. de Riaz figures as P. birmensdorfensis 

 (Moesch) ' show at a diameter of 51 mm. only forty-five costae ; 

 according to Siemiradzki, they do not, therefore, belong to Moesch's 



1 ' Description des Ammonites des Couches a, Pcltoceras transversarium de 

 Trept (Isere)' 1898, p. 27 & pi. x, figs. 6-7. 



