LIOCERAS OPALINUM. 53 



opalinum. This bed is called by him a " sandy blue-hearted limestone." Both 

 Mr. Walford and Mr. Sharpe quote Am. Murchisonce from the same bed as Am. 

 opalinus, but Mr. Walford informs me that he somewhat doubts this identification, 

 as well as that of Am. Iceviusculus which he gives, and I expect that the same must 

 be said of Mr. Sharpe's. The Lioceras opalinum at Hook Norton was associated 

 with a species of Hammatoceras (?), which Mr. Thompson also sent me from 

 New Duston, and which also occurs with Lioc. opalinum at Burton Braclstock, so 

 that probably there can be little doubt of the identity of this horizon (the Opalinum- 

 zone) throughout these Counties. 



I have thus gone somewhat fully into the position of Lioceras opalinum, 

 first because palseontological details are very insufficient unless accompanied, 

 wherever possible, with the full geological conclusions to which they lead us, 

 especially in the case of Ammonites, which have been used to designate the 

 zones ; secondly, the zone of Lioceras opalinum is more persistent and more 

 recognisable than perhaps any other in the Inferior Oolite ; and, thirdly, 

 because, lying as it does at or near the base of the Inferior Oolite, it is a most 

 useful geological landmark that ought to be fully established. I have verified its 

 occurrence in the Counties of Dorset, Gloucester, Oxford, and Northampton by 

 an examination of specimens of the characteristic Ammonites. 



Lioceras opalinum, var. comptttm (Beinecke). PI. XIII, fig. 11 ; PI. XIV, figs. 3, 



4, 5, 6. (PI. XIII, fig. 12; PI. XIV, 

 figs. 1, 2, 7, 8, 9 doubtful forms). 



1818. Nautilus comptus, Beinecke. Maris Protog., figs. 5, 6. 



1884. Habpocekas opalinum, Wright. Lias Ammonites, Pal. Soc, pi. 80, fig. 4. 



1885. — comptum, Haug. Beitrage Monog. Harpoceras, Neues Jahr- 



buch, Beil.-Bd. iii, p. 681. 



1886. opalinum, Vacek. Oolithe Cap San Vigilio, Abb. der k. k. 



geol. Reichsanstalt, Wien, Bd. xii, 

 No. 3, pi. vi, figs. 6, 7, 13, only. 

 1886. — ? MuECHisoNiE, Vacek (non Soiverby). Ibid., PI. vii, fig. 5. 



It is rather difficult from a mere examination of Reinecke's figure of Nautilus 

 comptus to say what it may be, and the identification should be regarded only 

 as the most probable until reference can be made to the original specimen if it 

 exists. That there is very great similarity between the little specimen, PI. XIII, 

 fig. 11, and Reinecke's original figure, cannot, I think, be denied. Dr. Haug con- 

 siders that what Dr. Wright figured as Lioc. opalinum with fascicled ribs (loc. cit.) 

 is the adult form ; but Dr. Wright placed Nautilus comptus as a synonym of 



