146 W. H. Hudleston — On the Yorkshire Oolites. 



one species, viz. Al. bispinosa,^ and even this was scarcely entitled to 

 appear, as there is no proof that it ascends above the Lower Calcareous 

 Grit. The repi'esentatives of the Brown Jura are somewhat better 

 off in this respect, the Dogger (zone 1), and the Kelloway Rock 

 (zone 5) contributing the greater number — of individuals certainly. 

 Owing to the difficulty of obtaining unmutilated specimens of these 

 easily broken shells, it has been found impossible to institute any 

 very close comparison with forms from other districts. However, 

 we can perceive that there is a general analogy in the respective 

 forms according to the several horizons, whilst in detail, especially in 

 the Inferior Oolite, there appears a considerable amount of difference, 

 thus necessitating the making a greater number of subspecies than is 

 altogether satisfactory. The forms which occur in the Dogger cannot 

 be exactly fitted either with those from Dundry as described by Mr. 

 Tawney, or with those from Bradford Abbas, etc., in my own 

 collection. Curiously enough, the Yorkshire Dogger and Millepore 

 Rock yield specimens more like Deslongchamps' Rostellaria hamus 

 than do the Dorset-Somerset beds. There are several specimens of 

 the hamus group, mostly small, — both from the Millepore Rock and 

 Scarborough Limestone, which are so badly preserved that they must 

 perforce go under the general designation of Alaria Phillipsii. 



The Kelloway Rock, which, as I have often pointed out, is a far 

 more comprehensive series than the Kellawaj's Rock of the South of 

 England, is our principal repository for the Oxfordian forms, and 

 here we obtain, in a spathic condition, fossils which in the clays of 

 the south are compressed and in a totally different mineral condition. 

 Some of these also appear as compressed casts in the Oxford Clay of 

 Yorkshire. The bispinosa-trijida group here seems to culminate. 



Subjoined is a table, where an attempt is made to show the groups 

 of Alaria and their distribution in the Oxfordian and Lower Oolites 

 of Yorkshire. 



1. The Samus-grovip (monodactyls) 



a. Alaria hamus, yar. Phillipsii, Dog., Mil., Sc.L. 



b. ,, unicarinata, Dogger. 



c. ,, pseudo-armata. Dogger. 



2. The bispinosa-trijida group (partly monodactyl, partly didactyl). 



a. Alaria bispinosa, var. elegans, Cornbrash. 



b. ,, ,, ,, pinguis, K. R. 



c. ,, ,, ,, communis, K. E,., L. C. G. 



d. ,, ,, ,, trijida, 'K.'Si., O.G. 



3. The Myurus-gxovL^ (didactyl). 



a. Alaria myurus, Millepore, Cornbrash. 



b. „ ,, var. teres, Cornbrash. 



4. The exhaustive division, — includes other forms whose affinities and specific 

 position are more or less doubtful. 



Out of these four groups there are two which, in Yorkshire, 

 are at once distinguished as characteristic of certain horizons. 

 All three zones of the Inferior Oolite, viz. the Dogger, Millepore 

 Rock, and Scarborough Limestone, are characterized by one or 

 other of the varieties of the liamus-^von^, and in no single instance 

 that has come to my knowledge has a specimen of any of the 

 1 Geol. Mag. 1880, p. 532. 



