50 W. IT. HncUeston — On the Yoyhshire Oolites. 



As regards the traces of a tootli said to exist in Thorent's species, 

 D'Orbigny's plate shows a strong callosity on part of the columella, 

 but no fictual tooth. 



In Mr. Leckenby's collection these fossils are labelled Nerita 

 lavigata, Phil, non Sow. : in the Scarborough Museum there is a 

 large specimen labelled Monodonta Icevigata, Phil, non Sow. This is 

 at least collateral evidence that Phillips's figure (xi. 31) refers to the 

 fossils now under consideration. Moreover, there are no other fossils 

 forthcoming which answer to the Phillipsian species. Whether 

 more than one species can be made out of the available specimens is 

 a point which cannot be absolutely decided, though I have preferred 

 to treat them as varieties. 



JDescriptioris. — Variety A. — Specimen from the Dogger (zone 1), 

 Peak (Blue Wyke). Leckenby Collection. Fig. 1. 



Width 15 millimetres. 



Spiral aBgle 110°. 



Shell turbinate, transversely ovate ; body- whorl large in proportion 

 to the spire. Whorls about four, depressed, somewhat flattened at top, 

 and separated by a wide and slightly channelled suture. Although 

 apparently smooth, the shell, on closer inspection, is seen to possess 

 a very fine and regularly undulating spiral ornamentation, decussated 

 by broad lines of growth, especially visible on the flanks of the 

 body-whorl. Aperture large and circular, but the anterior portion 

 concealed in the matrix. 



Another specimen. — Same horizon and locality. Jermyn Street 

 Museum. Fig. 2. 



Height 13 millimetres. 



Width 14 „ 



Spiral angle ? 



Eatio of body-whorl to entire shell about .... 80 : 100. 



The spire of this specimen is in worse condition than the one 

 previously described (Fig. 1) ; but the body- whorl is similar in shape 

 and ornamentation, and probably also in relative size. Being free 

 from matrix, the aperture is clear, though a portion of the outer lip 

 and anterior extremity is deficient. Enough remains to show that 

 the aperture was very wide and produced; with a long columella 

 very slightly curved and much thickened by callus. No umbilicus. 



Variety B. — Specimen from the same horizon and locality. York 

 Museum. Figs. 3 and 3a. 



Height 12 millimetres. 



Width 12 ,, 



Spiral angle 96°. 



Eatio of body-whorl to entire shell 70 : 100. 



Shell turbinate, subovate, imperforate ; body- whorl large in com- 

 parison with the spire, but less so than in variety A. The entire 

 shell consists of about five whorls, which are tumid, scarcely flattened 

 atop, and separated by a suture of moderate depth. (N.B. — The 

 appearance of a sort of belt over the suture, between the penult and 

 body-whorl, correctly represented in Fig. 3, has no structural 

 significance, but seems to be the result of one of those curious 



