178 INFERIOR OOLITE AMMONITES. 



given to palceontologists. Dumortieria radians, Bum. Moorei, Dum. subundulata, 

 Gramm. subserrodens, and this species have been considered merely as individuals 

 of one form called Am. Moorei ; and this form was not even allowed to be a good 

 species, but was, with many other species, considered merely as a variety of a 

 so-called Am. aalensis,^ or sometimes of Am. opalinus^ or occasionally these two 

 species were merged in one.^ 



Such opinions are partly due to the extraordinary convergences which arise 

 between these species — convergences brought about to a certain extent by the fact 

 of the same law of development governing these forms (p. 133 et seq.). 



This species has, more than any other, passed under the designation of 

 Am. Moorei, Lycett ; and it was only by a very careful comparison of certain 

 specimens with Lycett's original in the Museum of the Greological Survey — aided, 

 too, by Mr. E. T. Newton, who kindly developed the suture-line of that species 

 for me — that I was able to see that we really had to deal with two distinct species, 

 and actually, in spite of their great resemblance, with members of two genera — 

 the descendants of two different lines of ancestors whose common source is at any 

 rate not later than the lowest beds of the Lower Lias. 



It is both to this species and to Dumortieria Moorei mixed together* that I am 

 referring whenever I have mentioned Gramm. Moorei in the pages of the first 

 three portions of this Monograph (pp. 1 — 144). The resemblance of the two 

 species is so close that it is necessary not only for the specimens to be in 

 good preservation but for every feature to be clearly shown ; and even then it 

 requires not only great care but much experience to rightly separate these two 

 extraordinary species. In general the condition of the specimens found, whether 

 in the so-called Cephalopoda-beds of the Cotteswolds, or in the Yeovil Sands, is 

 far from satisfactory, so that the determination of many specimens cannot be 

 entertained. This remark applies equally to the majority of the Grammocerata 

 which have their chief location in these strata. 



Gramvioeeras mactra is not a common fossil. It occurs in that part of the 

 Opalinum-zone to which I have applied the term Moorei-heds, and consequently is 

 an actual companion of these species of Dumortieria which so closely resemble it 

 in all respects, namely, Dum. Moorei and Dum. subundulata. Whether they are 

 mimetic of this species, or vice versa, is an interesting point. It is also singular to 

 find that in the same bed we first met with Lioceras opalinum, a species having a 

 similar ornamentation of fine strige, which has led to its being considered more 



^ Lycett, " Ammouites of the Sands intermediate to the Upper Lias and Inferior Oolite," ' Proc. 

 Cotteswold Club,' vol. iii, 1805; also Wright, 'Monograph Lias Amm., Pal. Soc.,' p. 458, 1884. 

 2 Wright, ibid., p. 148, 1879. 



•^ Lycett's manuscript quoted by Wright, ibid., p. 465, 1884. 

 * For the differences see p. 162. 



