422 THE LIAS AMMONITES. 



irregular, both as regards the size and number of their foholes. The auxiliary lobes are- 

 placed at irregular distances apart and decrease in magnitude towards the innermost lobe, 

 which is quite rudimentary. 



Affinities and Differences. — Phyll. Buvignieri very much resembles Amm. lynx,. 

 d'Orb., in its compressed, extremely involute shell, with its almost occluded umbilicus, 

 and in the style and structure of the suture-line ; but though it wants the festooned carina, 

 and has a narrower umbilicus than Amm. lynx, the affinities are very close indeed. 



Locality and Stratigraphical Position. — This species is marked on the ticket, Belem- 

 nites-acutus zone, Ballintoy. I have a small specimen of this species, 5 millimetres in 

 diameter, which exhibits all the characters of the large and middle specimens. So it 

 appears to retain its specific form through life, the only difference I detect is that the 

 young shell is proportionately thicker and its siphonal area rounder than in the largfr 

 figured example with its subcarinated area. The figured specimen belongs to the Belfast 

 Museum. 



Phtlloceras Zetes, d'Orbigny, PI. LXXVII, fig. 1 — 3. 



Ammonites heterophyllus amalthei, Quenstedt, Cephalopoden, p. 100, pi. 6, fig. 



1, 1846. 



— Zetes, d'Orbiffny. Prodrome de Paleontologie, etage 



9, No. 55, 1849. 



— HETEROPHYLLUS Amalthei, Oppel. Der mittlere Lias Schwabens, p. 47, 



1853. 



— Zetes, Studer. Geologie der Schweitz, t. ii, p. 36,. 



1853. 



— — Von Sauer. Cephalopoden Nord-est Alpen, 



p. 56, pi. xviii, figs. 1, 3, 1856. 



— — Oppel. Die Juraformation, p. 169, 1856. 



Diagnosis. — Shell compressed, discoidal, highly involute ; umbilicus small, narrow, 

 open, exposing the inner whorls. Shell very thin, marked with delicate hair-like lines, 

 all inflected forward ; sides flattened, smooth ; siphonal area round ; lobe-line very 

 tortuous, developing from nine to eleven lobes. 



Dimensions. — The figured specimen: transverse diameter 180 millimetres; height of 

 the last whorl at aperture 100 millimetres ; greatest width near the spine 45 millimetres ; 

 width of umbilicus 20 millimetres. A larger specimen in my collection measures as 

 follows : transverse diameter 294 millimetres; height of last whorl at aperture 170 milli- 

 metres; greatest near spire 90 millimetres; width of umbilicus 30 millimetres. 



Description. — The HeterojjJiylliddB form a remarkable natural group closely related to 

 each other by form and structure, differentiated, however, by fairly-marked specific 



