424 THE LTAS AMMONITES. 



phjllum. Sow., found in the Upper Lias of Whitby ; the following differences I have 

 long observed after a careful comparison of many good examples with each other : 



1st. The shell is much more compressed in Vhyll. Zetes than in PIit/U. heterophyllum . 

 The sides are much flatter, and the siphonal area narrower. 



2nd. The umbilicus is wider in Fhyll. Zetes, and permits all the inner whorls to be 

 seen, whilst in Fliyll. heterophyllum the umbilicus is almost occluded. 



3rd. The suture-line consists of a much more angular tracery, a finer subdivision of 

 the parts of the lobes, and much smaller folioles in the saddles than what we observe in 

 Phyll. heteropliyllum. Any one in the habit of studying these shells has no difficulty in 

 deciding on the species from an examination of the suture-line alone. In figs. 3 and 4 

 I have given accurate drawings of the suture-line in the two species for comparison. 



4th. The lines of growth on the shell are more marked in Phyll. heterophyllum, and the 

 wonderful fan-like folded expansion of undulating ribs, which I have for the first time 

 delineated in PI. LXXVIII, fig. 1, and which characterise the body-chamber of Fhyll. 

 heterophyllum have not yet been observed in any of the fine examples of Fhyll. Zetes 

 hitherto collected. 



Locality and Stratiyraphical Position. — My specimens of Phyll. Zetes were obtained 

 from the Amal. spinatus-hed at South Petherton, Somersetshire, and from the same 

 horizon at Grettan, Gloucestershire. In Swabia, according to Dr. Oppel it is found at 

 Breitenbach, with Am. amaltheus yiycis, and in a rich pyritic bed at Bachs, and near 

 Sondelfingen in the Baling region. Von Hauer obtained his fine example from the 

 dark red limestone of Enzesfield, North-eastern Alps. Studer reports many localities 

 in the Bernese Alps of Switzerland, where he has found this species ; and Meneghini 

 collected a specimen in the Upper Lias of Sibilla and a broken fragment at Spezzia. 



Dr. Oppel collected one specimen from the Middle Lias of Normandy. Its lobes are 

 so different from those of the true Phyll. heterophyllum, Sow., that he was convinced 

 a separation from that species was necessary, and this he carried out in his ' Jura- 

 formation,' p. 169. 



Phylloceras heterophyllum, Sowerhy. PI. LXXVII, fig. 4 ; PI. LXXVIII, figs. 1, 2. 



Ammonis cornu, Martin Lister. Syiiops conchyliorum, (Edit, alt.) 



tab. 1049, fig. 24. 1770. 

 — NAi'TiLiTEs, J. Baier. Oryctogr. noric, p. 60, tab. ii, fig. 1, 1708. 



Ammonites heteeopiitllus, Sowerby. Mineral Conchology, pi. 266, 1820. 

 Nautilus Wiiitbiensis, Toung and Bird. Geol. Yorkshire Coast, PI. xiii, 



fig. 1, 1822. 

 Globites heteeophyllus, Haan. Ammon. et Goniat., 148, 1825. 



Ammonites — Phillips. Geology of Yorkshire, pi. xiii, fig. 2, 1829.- 



— — Hartmann. Versteiner. Wiirtemb., p. 21, 1830. 



— — Buckland. Bridgewater Treatise, pis. 38, 39, 1S36. 



