LIOCKRAS PALI NUM. 41 



original figure. This specimen came from bed No. 5 of the Coaley-Wood section 

 (p. 45). Fig. 6 is a very small specimen of the typical form, for comparison with 

 fig. 11, and indicating that the typical form is constant in its ornamentation 

 throughout life. This specimen is from Burton Bradstock, Dorset. Figs. 7, 8, 

 give a variety, slightly thinner and having a considerably larger umbilicus. This 

 form is rather the commonest of all. In Fig. 8 is indicated the outer portion of 

 the ventral area on the top of the figure, peculiarly compressed, probably due 

 in part to absence of test. Figs. 9, 10, illustrate a younger form of this kind. In 

 figs. 7 and 9 the peculiar, much sloped inner margin, which gives the specimens 

 a singular appearance, is scarcely brought out. These specimens are from Hares- 

 field Hill, bed No. 15. The fig. 1 at p. 36 displays the suture-line of this species; 

 it was taken from a large adult specimen, and must be considered as typical for 

 the genus Lioceras. 



Lioceras opalinum is an Ammonite which has given its name to a certain zone 

 or series of strata lying between the Jurense-zone below and Murchisonce-zone above ; 

 and this horizon with the beds below, the Sands especially, down to the Upper Lias 

 Clay, has caused much debate whether it should be classed with the Lias or the Oolite. 

 At pages 2 — 5 I have given a few notes upon the subject, and the opinions of some 

 authors ; but, as I had not then seen the sections in Gloucestershire where this 

 zone is exposed, and had only been able to obtain an imperfect view of those in 

 Dorset, I purposely refrained from giving any opinion as to the desirability of 

 classing the Opalinum-zone with the Lias as Dr. Wright had done, or with the 

 Inferior Oolite (or at any rate distinct from the Lias) as most other authors have 

 been inclined to do. Since, however, I have had opportunities of thoroughly 

 examining the Gloucestershire sections at Frocester, Coaley Wood, Cam Down, 

 &c, and especially at Haresfield Hill, I have come to the conclusion that the 

 sections in Gloucestershire furnish no reason at all for classing the Opalinum-zone 

 otherwise than in accordance with what has been, I believe, the usual custom, 

 namely, as distinct from the Lias. Dr. Wright, at p. 148 of his ' Monograph on 

 the Lias Ammonites,' gives "a thin band of hard ferruginous marl" as the 

 Opalinum-zone at Haresfield, and states that he had found a piece of rock which, 

 itself containing Inferior- Oolite fossils, had on its underside an impression of 

 Harp, opalinum. Since, however, I have found most of my specimens of this 

 species in this rock I cannot do better than clearly point out the position which 

 Lioceras opalinum occupies. The following sections not only show the relation- 

 ship of the Opalinum-zone to the beds above it, but also, through the Sands to the 

 Upper Lias Clay below ; and, since we shall have to discuss several species of 



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