LIOCERAS CONCAVUM. • 63 



of the same species which occur in the Concavum-hed in Dorset. The most typical 

 species are Bhynchonella Forbesi, Dav., Rh. liostraca, S. Buckm., Terebratula Eudest, 

 Oppel, and T. cortonensis, S. Buckm. 



It was doubtless on account of the abundance of the various forms of Lioceras 

 concavum, and the well-defined horizon of which they are characteristic, that Mr. 

 Hudleston, when giving a very complete account of the Inferior Oolite of Dorset, 

 in his Monograph on the Gasteropoda, 1 called these strata the Concavum-heds 

 rather than the Sowerbyi-zone. The reasons which he gives for this are certainly 

 most cogent ; and I will now state why I adopted his suggestion. 



I have lately had the opportunity to visit the sections at Dundry Hill, and to 

 examine in the Bristol Museum Sowerby's figured specimen of Am. Sowerbyi, 

 and the matrix, from which it was extracted, preserved with it. 2 This matrix 

 is certainly not the same as that from which the Dundry specimens of 

 Lioceras concavum in the Museum appear to have been obtained. I have always 

 noticed the scarcity of Am. Sowerbyi in Dorset, and it seems to be equally scarce 

 at Dundry Hill, for there were no other specimens in the Museum. During the 

 short time at my disposal I was unable to determine the actual horizon at Dundry 

 Hill occupied by either Lioceras concavum or Am. Sowerbyi, but, considering all 

 the evidence, I had certainly some doubts whether they occurred together. It is 

 possible that the true Am. Sowerbyi may really occupy a somewhat higher horizon 

 than that of Lioceras concavum? and yet be below the Sauzei-zone, 4, and that such 



1 Pal. Soc, vol. xl, for year 1886. See also " Excursion to Sherborne " by the same author, ' Proc. 

 Geol. Assoc.,' vol. ix, p. 191, 1887, for much information concerning these beds generally. 



2 'Mineral Conchology,' pi. 213, lower figure. The original Am. Sowerbyi evidently came from 

 the Ironshot Oolite, which yields specimens of Steph. Humphriesianum. 



3 Since the above was written the advent of more specimens of Dundry Ammonites through the 

 persevering energy of my kind friend Mr. E. Wilson, E.G.S., has enabled me to say that Am. Sowerbyi 

 and Lioceras concavum occupy two different horizons, a fact which may be deduced from the matrix 

 peculiar to each species. Lioc. concavum occurs in the lower position, viz. in the series of strata 

 which underlie by some two feet the well-known "Ironshot Oolite" (ITumphriesianu?n-zone?) of 

 Dundry Hill. These strata are about six feet thick, and may be described as a most irregular 

 series of bluish-grey, very slightly oolitic, nodular ragstone embedded in yellowish-brown marl. 

 Sometimes the stone so preponderates that the marl appears merely as partings. The two feet lying 

 between the ragstones and the " Ironshot " consist of whitish stone with a few iron grains, which are 

 more plentiful than in the former, but less so and smaller than in the latter. 



On trying to correlate the Dundry strata with those of Dorset, and the strata of both localities 

 with those of the Continent, it appears to me that the Concavum-beds must occupy an horizon inter- 

 mediate between the series of strata known on the Continent as, respectively, the Murckisonce-zone 

 and the Sowerbyi-zone, and that they (the Concavum -beds) are absent upon the Continent. Iu 



* Where the Sowerbyi- and Sauzei-zones are well developed, as would appear to be the case in 

 certain localities on the Continent, it may be possible to separate them distinctly ; but at Dundry 

 we find peculiar conditions, because it would appear that Am. Sowerbyi, Am. Sauzei, and Am. 

 JIumphriesianus occupy the same horizon. Perhaps the name Sowerbyi-zone will have to be dropped, 

 there having been considerable misconception regarding the type-form of the species. 



