38 INFERIOR OOLITE AMMONITES. 



forms with seemingly small differences (especially when badly preserved), but 

 in my opinion these forms can be shown to be descended from most different 

 sources and to possess certain constant differences both in structure and detail. 

 To put Am. Moorei, aalensis, and opalinus (if correctly identified) into the same 

 species is to ignore their true affinities, to entirely overlook the differences in their 

 suture, the different shape and flexure of their ribs or striae, their different mode 

 of growth, as well as their different parentage. An attempt to unite as one species 

 Am. opalinus with Am. concavus, Sow., or Am. elegans, Young, would, I think, 

 be more reasonable, but not such a species as Am. opalinus with either Am. 

 Moorei or Am. aalensis. 



From nearly all the other species of the genus Lioceras this species is 

 separated by an entire absence of ribs at all ages, by the possession of numerous 

 very fine hair-like sigmoidal striae, more prominent than mere lines of growth, and 

 produced on the ventral area more than is usual with other species of this genus. 

 Its small umbilicus showing portions of the inner whorls is also distinctive. 



Probably considerable difficulty may be experienced in appreciating the differ- 

 ences which exist between Lioceras opalinum and Am. elegans, and therefore a few 

 words to try and put the matter in as clear a light as possible may not be out of place. 

 The first thing, however, is the correct appreciation of what Am. elegans really is, 

 and on this point much confusion has existed. Sowerby was the first to figure 

 and describe Am. elegans, and palaeontologists have always experienced considerable 

 difficulty in deciding what the species actually is that he so figured. As it does 

 not come within my province to write a full account of this species, with the various 

 views that have been adopted, I only say that I believe the specimen figured by 

 Sowerby has a hollow carina and belongs to the true Falciferi, i. e. Harpoceras 

 falciferum, Sow., subplanatum, Oppel, &c, and consequently belongs to a genus 

 entirely different from Lioceras, namely, to the genus Harpoceras restricted} Subse- 

 quently Young and Bird gave a not very intelligible figure of an Ammonite under 

 the name elegans, but this is not Sowerby's species. Dr. Wright, being unable 

 to identify Sowerby's species, retained the name elegans, for Young and Bird's 

 species ; and the specimen he figured on PI. LIII, figs. 1, 2, 3, he described in 

 his text as Harpoceras elegans, Young (non Sowerby). Taking this figure as 

 really representing Young and Bird's species, I believe that it evidently differs 

 from Am. elegans, Sowerby, and belongs to the genus Lioceras; and hence we 

 may now retain the name. Then from Lioceras elegans (Young) Lioc. opalinum is 

 distinguished by possessing fine strise during the whole of its growth, by possessing 

 a much less acute carina, and a more compressed ventral area. Probably the best 

 distinction is the possession of fine falciform ribs by the young forms of Lioceras 



1 " On Jurassic Ammonites," S. S. Buckman, ' Geol. Mag.,' dec. iii, vol. iv, No. ix, 1887, p. 397. 

 Harpoceras is here used only for the true Falciferi. 



