(part 1] OF THE SHALES-WITH-' BEEP.' 67 



discuss the phylogenetic relations of some of the ammonites of 

 the Lower Lias. The development of a number of important types 

 here dealt with, for instance, Arnioceras, Agassiceras, Arietites, 

 Cymbites, JCipheroceras, Microderoceras, etc., was studied some 

 years ago ; but only brief reference can be made to this onto- 

 genetic work, and it is also impossible at present to figure the new 

 forms here recorded. It is a matter for regret that, in the absence 

 of detailed stratigraphical work and careful zonal collecting for 

 other districts, exact correlation is as yet impossible ; and, for this 

 reason, but little help was obtained from a study of the splendid 

 ■collections in the British Museum (Natural History), of the 

 genus Arnioceras, from Yorkshire and the Midlands, for instance. 

 On the other hand, my Arnioceras material from Skye, described 

 separately, 1 proved of use, and confirmed what, so long ago as Du- 

 mortier's time, was surmised of the enormous range of this genus, 

 although sufficient emphasis had not been laid upon it in previous 

 accounts of the Dorset succession. Also, a collection made by the 

 late Sir Henry Butlin, and recently presented to the British 

 Museum (Natural History), contains a number of ammonites from 

 Stockton in Warwickshire; and, since some of them were collected 

 in place and their occurrence was carefully noted, it has been 

 possible to obtain from them additional valuable information. 



Unfortunately, the preservation of most of the ammonites in 

 the Shales- with- Beef is bad, and many species of Arnioceras, as, 

 for example, ' A. obliquecostatum,'' are based only on the character 

 of the ribbing on the outer whorls, obviously a most unsatisfactory 

 criterion. The same remark applies to ' Arnioceras mendax, var. 

 rariplicata ' Fucini. A specimen collected at Redcar, not in situ, 

 but associated with ' Ammonites ' cf. latesulcatus Quenstedt, and 

 Arnioceras cf. arnouldi (Dumortier), which probably come from 

 below the gmuendense subzone, also agrees externally with 

 the Italian form : the suture-line, however, is quite different, 

 for, while the suture-line of the Italian species resembles that 

 of the Gloucestershire A. nodulosum (J. Buckman), that of the 

 Redcar specimen agrees with the suture-lines of A. hartmanni 

 (Oppel), as here interpreted, A. semicostatum (Young & Bird) 

 and A. nigrum (Blake), all late forms. The resemblance based 

 on ribbing is probably quite accidental, hence the difficulty of 

 naming the badly-preserved Dorset specimens here dealt with. 

 Another crushed form, from bed 70, was at first identified as 

 JEtomoceras scipionianum (A. d'Orbigny), and, being associated 

 with many large ' Goroniceras ', suggested a horizon far too 

 low in the sequence. But Agassiceras proved to be common in 

 the strata below, so that it was clear that bed 70 must be above 

 and not below Mr. Tutcher's sauzeanum zone or horizon I of the 

 Harzburg Ironstone. The ' AEtomoceras ' just mentioned is thus 

 probably a laterally-flattened crushed Agassiceras, comparable 

 to Reynes's 3 Ammonites multicostatus SoweiOjy, var. spinaries 



1 'On Lower Lias Ammonites from Skye ' Geol. Mag. 1922, pp. 170-76. 

 a ' Monographic des Ammonites ' 1879, pi. xxiv, fig. 25. 



r2 



