LIOCERAS OPALINUM. 37 



(Plate IV, fig. 8), and of Lioc. v-scriptum (Plate IX, fig. 4), agree exactly with the 

 suture here shown. I have found, too, that the sutures of all the species of Lioceras 

 agree in a remarkably exact manner with this pattern. I shall, later on, have more 

 to say on this point when figuring and discussing them in comparison with those 

 of other genera. Dr. Wright, in his Monograph ' Lias Ammonites,' Plate LXXX, 

 has mistaken the suture-line of this species, as I have pointed out in the ' Geological 

 Magazine.' 1 



On account of the additional material which is being constantly obtained for 

 the purpose of this work, it unfortunately cannot be avoided, that both in the plates 

 and the letterpress, certain species are placed somewhat out 'of order, although in 

 the letterpress, and as far as possible in the plates, the sub-groups will be kept to 

 themselves. 



A short time ago, at the commencement of the present year (1887), I possessed 

 only a few small specimens of Lioceras opalinum from Dorset. Having now 

 obtained a fine series from Gloucestershire, with many new features, I consider it 

 necessary to give a further account of this species (see Dr. Wright's Monograph, 

 loc. cit.), and thus more fully complete the series of species belonging to the genus. 



It is very singular that in the Cotteswold district so much confusion should 

 have always prevailed as to the proper characteristics of this species, and so much 

 desire should always have been expressed to include other totally different species 

 in this or to merge it in others. At p. 148 of his Monograph Dr. Wright 

 regarded Lycett's Harp. Moorei as a variety of Harp, opalinum ; but afterwards 

 he figured them for comparison on the same plate, considering Lycett's species to 

 be a synonym of Zieten's Am. aalensis. Dr. Lycett, too, has been quite willing to 

 drop his own species, for in some MS. notes, which Dr. Wright quotes in extenso 

 (pp. 465, 466), and which, by the kindness of Mr. W. C. Lucy, F.G.S., I have seen, 

 he has considered it correct to place Am. aalensis, Moorei, costula, and other forms 

 as synonyms of Am. opalinus. Several reasons may be given as contributing to 

 form this opinion ; first, the condition in which the Cotteswold Ammonites 

 frequently occur is such as will not allow of an examination of their more minute 

 characters ; next, the number of apparently very similar forms which occur 

 together in a thin series of strata ; and especially the fact that probably the 

 identification of one or two of the chief species has been more or less loose and 

 incorrect. Dr. Lycett almost admits as much in his MS. notes, when he says 

 that no specimen of Am. opalinus has rewarded his efforts at Frocester Hill; 

 and none of the specimens figured by Dr. Wright as Harpoceras aalense appear to 

 me to belong to Zieten's Am. aalensis. Probably, therefore, the argument is 

 founded on an unsound basis. No doubt there is a perplexing number of 



1 'The Lobe-line of certain Lias Ammonites,' S. S. Buckman, ' Geol. Mag.,' dec. iii, vol. iii, 

 No. 10, 18S6, p. 442. 



