338 me. l. f. spath on the [Dec. 1914,. 



the Green Ammonite Beds, larger specimens again occur, closely 

 resembling Tr. loseombiin dimensions and suture -line, but differing 

 in a slightly crenulated periphery (No. 13 in Table II). Now 

 Tr. paucicostatum, which Pompeckj (1893, p. 11) records from 

 the Ibex Zone, is very similar, and differs but slightly in suture-line 

 and in having a larger umbilicus. Woodward & Ussher (1911) 

 record Liparoceras becliei (Sow.) 1 from the Belemnite-Stone,. 

 and other specimens of true Lipocerata have been found at this 

 horizon ; the evidence as to the age of the beds afforded by the 

 forms of TragopJiylloceras is unsatisfactory, and the boundary 

 between the Ibex and the Davoei Zones cannot yet be definitely 

 fixed. Crenulation of the venter, as we shall see later, is anagenetic 

 in the forms of the Ibex Zone as w r ell as in the high-zonal forms 

 from Golden Cap and Seatown (Nos. 9 & 10 in Table II, p. 343), 

 and even in body-chamber fragments from the zone of Amalthevs 

 margaritatus. The horizon of these beds will be reconsidered 

 when their segoceratid ammonites, which are of greater zonal 

 value, are dealt with. 



The points, then, to be noted are, first, that TragoplujUoceras 

 loscombi has its greatest development at the horizon of Deroceras 

 davcei, although it persists into margaritatus times. Secondly, 

 that the small, immature ammonites are mostly higher than the 

 Ibex zone, and at any rate not associated with Acantliopl ev rocera s , 

 which occurs immediately below the base of the Green Ammonite 

 Beds. It should be added that, unfortunately, the mode of preser- 

 vation of the larger specimens of Tr. loscombi prevents a direct 

 comparison of their inner whorls with the small casts occurring 

 in such abundance in the clays. 



SoAverby's description and figures are reasonably good, though he 

 gave no section, and the thickness of the shell could be gathered 

 merely from his remark ' Thickness being only one-third the 

 length ' (of the aperture) ; but this is not quite correct. In fig. 1 

 of PL XLIX the sectional view of Sowerby's type-specimen is 

 reproduced, and it will be seen that it differs from the section of 

 A. d'Orbigny's ammonite (1842, pi. lxxv, fig. 2). Pompeckj (1893, 

 p. 13) thought that the latter was, perhaps, not the same as 

 Sowerby's. In the British Museum collection, however, there is a 

 specimen (No. 37181, Coll. Tesson) from Vieux Port (Calvados), 

 which is a topotype of some of A. d'Orbigny's specimens, and differs 

 in no particular from the English type. Furthermore, Prof. Paul 

 Lemoine kindly informed me that A. d'Orbigny's type-specimens 

 preserved in the Museum d'Histoire Naturelle (Collection de Pale- 

 ontologie) are in a mediocre state- of preservation, and somewhat 

 flattened and deformed artificially. Since d'Orbigny did not give 

 the locality 01 his figured specimen, it is of course impossible now 

 to identify it with certainty; but the specimen that seems to 

 ■ 



1 I -was kindly permitted to examine this specimen in the collection of the 

 Geological Survey, but it cannot be identified closer than as Liparoceras sp. 

 It cannot be A. becliei (Sow.), which occupies a higher horizon. 



