424 THE LTAS AMMONITES. 



pTiyllum, 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 Fhyll. Zetes than in PJiyll. heterophyllum. 

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



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

 seen, whilst in Pliyll. JieteropJiyllmi 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 

 PTiyll. heteropJiyllum. 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. heteropJiyllum, 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 Phyll. 

 heterophyllum have not yet been observed in any of the fine examples oi Phyll. Zetes- 

 hitherto collected. 



Locality and Stratigrapliical 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 yiyas, 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 frotn 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. 



Phtlloceras heterophyllum, Sowerhy. PI. LXXYII, fig. 4 ; PI. LXXVIII, figs. 1, 2. 



Ammonis coknu, Martin Lister. Synops conchyliorum, (Edit, alt.) 



tab. 1049, fig. 24. 1770. 

 — NAUTILITES, J. Baier. Oryctogr. noric, p. 60, tab. ii, fig. 1, 1708. 



Ammonites heteeophtllus, Sowerhy. Mineral Conchology, pi. 266, 1820. 

 Nautilus Whitbiensis, Young and Bird. Geol. Yorkshire Coast, PI. xiii, 



fig. 1, 1822. 

 Globites heteeophyllus, Haan. Ammoo. 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, 1836. 



