296 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 18, 



chifera. Ammonites Henleyi, Sow., A. latieostatus, Sow., and several 

 other species characterize the Belemnite-beds and some of the beds 

 immediately above them. Ammonites Davoei, Sow., occurs only in the 

 Green Ammonite-beds, in the uppermost layer alone of which is found 

 the form locally known as A. brevispina. A. margaritatus, Montf., 

 appears with the sand and mica in the " Three Tiers," and disappears 

 again with a deposit of marl ; its place is, however, on the recurrence 

 of sand, supplied by a closely allied form, A. spinatus, Brug. This 

 species is succeeded by A. serpentinus, Rein., and that again by 

 A. bifrons ; after which is a wide gap assignable to no particular 

 form. Above this interval A. Jurensis occurs, underlying the zones 

 of the Inferior Oolite. But though these and most Ammonites have 

 their zones well marked and restricted, it is not so with all. For 

 instance, A. Loscombii appears with A. Henleyi, abounds with A. 

 latieostatus, and goes some way up into the range of A. margaritatus, 

 where it makes its last appearance in the layer of small nodules 

 below the shelly marl. It thus passes through most of the grey 

 marls, but does not reach to the permanent appearance of the sand. 

 A. Jlmbriatus and A. Bechei are still less restricted, the latter ap- 

 pearing in the Belemnite-beds, and showing itself, in occasional 

 specimens, as far up as the sands of the ' Spinatus-zone ' ; the former 

 ranging still more widely, from the same starting-point up to the 

 very summit of the Middle Lias. These forms are thus found not 

 only in strata some hundreds of feet apart, but in the highest and 

 lowest of a series of at least four of the more restricted ranges. 



But if the ranges of the Ammonites are not very limited, neither 

 I apprehend are those of some of the other Cephalopoda ; Nautilus 

 semistriatus I find ranging coextensively with Ammonites Bechei, and 

 I cannot distinguish some of the Belemnites of the Marlstone from 

 those of the Belemnite-beds. 



In the Gasteropoda and Conchifera we find the vertical ranges of 

 several species of very various extent ; but they do not appear to me 

 to coincide so much with the distribution of particular Ammonites as 

 with other accidental circumstances. The Conchifera of theBelemmte- 

 beds occur also in the Green Ammonite-marls, but not in the shell- 

 bed under the sand, excepting such a ubiquitous form as Plicatula 

 spinosa, Sow. Some of the Gasteropoda, on the other hand, occur 

 also in the Pleurotomaria-bed associated with Ammonites spinatus. 



The Shell-bed under the Starfish-bed has, as I have said before, 

 many forms peculiar to a zone lying above the frequently mentioned 

 " layer of small nodules " and below the sands, but many of its 

 species occur again above, and these are represented by far finer spe- 

 cimens in the sands. It would thus appear that Ammonites marga- 

 ritatus occurs in two faunas, which, though blending together at their 

 junction, are yet very distinct. In the lower part of the ' Spinatus- 

 zone ' there appears to be a different fauna from that of the sands 

 below, and in its upper portion occurs the most remarkable collection 

 of Mollusca of any in the Lias. Along with many new and curious 

 forms are others that I have observed in some one or other of the 

 Middle Lias beds below. And yet, with all the diversity in the extent 



