194 W. S, Sudleston — On the Yorkshire Oolites. 



but higher np in the Jurassic rocks they seem to be very fairly 

 separable for such a genus as Alaria, which is so j)rone to effect 

 changes in its shell. Such was doubtless the opinion of Morris, 

 who quotes Al. hispinosa from the Lower Calc. Grit and Kel. Rock, 

 whilst Al. trifida is quoted as a distinct species from the Oxford 

 Clay and Kel. Rock of Yorkshire, the Great Oolite form being 

 referred to a variety. 



As far as the beds of Oxfordian age testify, and it is in these alone 

 in Yorkshire that either species occurs, Phillips and Morris were 

 justified in separating them, and it remains for us to decide how far 

 the specimens available bear out their views. Until this question 

 is settled it would be useless attempting to follow the mazes of the 

 Continental synonymy. Certain it is that forms with much resem- 

 blance to the well-known Oxfordian Al. trifida occur both in the 

 Inferior Oolite of Normandy and of the south of England. When 

 a rational system of nomenclature prevails, such forms will receive 

 an appropriate distinction under the chief group. At present, we 

 must be satisfied to hunt up and down the pages and plates of such 

 a work as Piette's for some haphazard title to bestow upon our fossils. 



Description. — Specimen from the Kelloway Rock (zone 5), Scar- 

 borough.^ Leckenby Collection. Plate VI. Figs. 11, 11a. 



The body-whorl, including the greater part of the tail, and the 

 penultimate, is all that remains, but these are in an excellent state of 

 preservation. In the penultimate the keel is almost exactly in the 

 middle of the whorl, very large and not at all sharp; anterior portion 

 of whorl but slightly constricted, and rising again to a slight basal 

 belt before reaching the suture, which is rather wide. The system 

 of spiral lines is exceedingly fine, and scarcely traceable in the 

 body-whorl below the anterior keel. The bodj^-whorl developes 

 two large, thick, but not sharp keels, which ai'e nearly of equal 

 strength. The posterior keel, owing to the shape of the whorl, is 

 rather the most prominent ; but the anterior keel is the stoutest, and 

 carries the most important digitation. In this sj)ecimen the upper 

 digitation is entirely broken away. Faint spiral strise may be noted 

 on the lower keel, which is also very slightly notched, corresponding 

 to a system of fine axial strige, which ornament the wing and base of 

 the body-whorl. The tail, or canal-sheath, is connected with the 

 lower finger by an expanse of wing, and itself commences to curve 

 almost immediately. Termination imperfect. 



Specimen from the same horizon, locality and collection. Plato 

 VII. Figs. 1, la. 



Length 20 millimetres. 



Width of last whorl to length of shell 45 : 100. 



Approximate spiral angle 34°. 



Although there is far more of this specimen preserved than of the 

 last, yet the condition is scarcely so good. The body-whorl with its 

 two lateral digitations and tail curving at once from the spire give 

 ua an excellent insight into the characteristics of Alaria trifida, as 



1 On the very same piece of stone occurs the specimen of Al, hispinosa, Plate VI. 

 Figure 9 : hence a good opportunity for comparison. 



