422 THE LIAS AMMONITES. 



irregular, both as regards the size and number of their folioles. The auxihary lobes are 

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

 which is quite rudimentary. 



Affinities and Differences. — Tliyll. Buviynieri very much resembles Amni. 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 Stratiyraphical 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 large 

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

 Museum. 



Phylloceras Zetes, d'Orbiyny, PI. LXXVII, fig. 1 — 3. 



Ammonites heterophyllxjs amalthei, Quenstedt. Cepbalopoden, p. 100, pi. 6, fig. 



1, 184G. 



— Zetes, dOrUgmj. Prodrome de Paleontologie, etage 



9, No. 55, 1849. 



— HETEKOPHYLLUS Amalthei, OppeL Der mittlere Lias Schwabens, p. 47, 



1853. 



— Zetes, Stiider. Geologic 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 ISO millimetres; height of 

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

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

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

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



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

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



