HILDOCERAS BIFRONS. 113 



identical in age with the sands at Midford, 1 have been lately replaced by some 

 authors in the Inferior- Oolite Series. 2 Another reason is that since these Sands 

 have been the subject of so much discussion, and since I have to introduce other 

 species which occur in them — species not included in Dr. Wright's ■ Lias Monograph' 

 — it is as well that the Ammonite-fauna of this deposit should be fully represented. 

 This genus also seems a good introduction to the next, namely, Poecilomorphus. 



The peculiarity about this variety is that it is so much compressed, and that 

 the inclusion of the preceding whorl is much greater than is usual in the species, 

 being up to the longitudinal furrow on the sides, and thus producing a smooth 

 umbilicus. I did not feel it necessary, or consider it justifiable, to take up much 

 room with a figure of this variety ; but the larger specimens, which reach 4| to 

 5| inches in diameter, show the same characteristic compression and inclusion. 



It is noticeable that these characters seem to be peculiar to those specimens 

 found in the Sands, and practically to be universal among them. The ribbing is 

 frequently very fine, like that shown by the figured specimen ; but there is some 

 variation in this respect. The test is usually well preserved, and is very thick on 

 each side of the carina, so that the furrows, which are deeply marked upon the core, 

 are scarcely perceptible on the test. 



The manner in which the indurated rock-bed in the Cotteswold Sands is filled 

 with specimens of this variety would seem to indicate that Hildoceras bifrons, at 

 any rate, was able to survive the change to conditions necessary to deposit a fine- 

 grained yellow micaceous sand (occasionally hardened into bluish-grey rock) instead 

 of a blue clay. 



That Hildoceras bifrons had been recorded from the Cotteswold Sands previous 

 to my notice of it last year (p. 45) was unknown to myself and to those to whom 

 I mentioned the subject. Nevertheless just thirty-one years previously, namely, 

 in 1856, the members of the Cotteswold Field Club were much surprised when 

 Dr. Wright announced that he had discovered the species in the Sands at Frocester, 

 and brought it forward as strong evidence for the Liassic character of what were 

 then known as the " Inferior-Oolite Sands." This discovery was alluded to in the 

 President's Address, 3 and in a paper on the Oolites of Gloucestershire 4 the 

 conclusions drawn by Dr. Wright are contested. 



1 See above, p. 50. From further research I find that the Yellow Sands near Midford belong to 

 the upper part of the Slriatulum-beds. The Cotteswold Sands are altogether below the Striatulum- 

 beds, and contain an Ammonite-fauna different to that of the Sands at Midford. There are no Yellow 

 Sands at Midford below the Striatulum-beds. 



2 II. B. Woodward, ' Geol. England and Wales,' 2nd edition, 1880, p. 285. But see this Mono- 

 graph, p. 50. 



8 Made by my father, as Secretary, at the President's request, January 27th, 1857. See also 

 Dr. Wright on " The Upper Lias Sands," ' Quart. Journ. Geol. Soc.,' vol. xii, 1856, p. 305, &c. 



* " The Oolites of Gloucestershire and North Wilts," by Prof. J. Buckman, ' Quart. Journ. Geo). 

 Soc.,' vol. xiv, p. 103, 1858. 



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