W. S. HucUeston—On the Yorkshire Oolites. 295 



The type specimen is especially valuable as showing ns the base 

 of '■ Trochits'" pyramidatus in a good state of presei'vation. This is 

 moderately concave, the chief depression occurring somewhat outside 

 the centre, the base rising again towards the columella. The um- 

 bilical region is marked by a shallow depression, exhibiting the 

 rudiments of an umbilical groove. The periphery is plain, but the 

 base itself is ornamented by a system of fine radial lines, while here 

 and there a few spiral lines may be noted. Aperture very oblique. 



Anothe}' specimen. — From the same horizon and locality. Leckenby 

 Collection. Figs. 3a, 36. 



Heiglit 17 millimetres. 



Width 25 ,, 



Spiral angle 86°. 



The sides are less abraded than in Phillips's type : consequently 

 the excavation of the posterior part of the whorls is more apparent, 

 and the somewhat flexuous ribbing is better seen. The body- whorl 

 is devoid of this ribbing and shows the scaly or lamellar structure 

 more plainly in consequence. The base is not well preserved, but 

 the periphery was evidently plain, and there are no obvious traces 

 of an umbilicus. 



Relations and Distribution. — Phillips's species is perhaps not exactly 

 the same as " Trochus " lamellosus. D'Orbigny's figures show the 

 ribbing as continuous throughout the body- whorl, though the descrip- 

 tion is perhaps compatible with its absence. We have already seen 

 that Lycett regarded them as identical. Making due allowance for 

 difference of matrix, the original differences were probably only such 

 as might be expected to occur in areas wide apart. All specimens 

 of Oaustus are represented by D'Orbigny as being more umbilicated 

 than are the Yorkshire ones. 



Onustus pyramidatus is not very uncommon in the Dogger, though 

 really good specimens are extremely'' scarce. It may generally be 

 distinguished from 0. ornatissimus, even in bad specimens, by the 

 closer pattern of the ribbing. This species is quoted by Lycett from 

 the Supra-Liassic Sands and Inferior Oolite of Gloucestershire. Mr. 

 Tawney does not mention the occurrence of Onustus at Dundry, but 

 I have evidence that specimens of an Onustus marked like lamellosus 

 {i.e. pyramidatus) occur in the Inferior Oolite of Dorset. 



Genus Nerita, Linueeus, 1758. 



The Inferior Oolite of Yorkshire contains three species which 

 seem fairly referable to the genus Nerita. One species occurs 

 sparingly in all three zones, but the other two would seem, according 

 to my present knowledge, to be confined to the Dogger. Of these 

 the only one at all abundant is Nerita minuta (i.e. tumidida). The 

 occurrence of any Nerite in the Yorkshire Oolites above the Inferior 

 Oolite is unknown to me : accordingly none were described in the 

 " Corallian Gasteropoda." As regards its occurrence on lower 

 horizons, we find that Tate and JBlake describe a single species, 

 Nerita alternans, from the spinatus-zone of the Yorkshire Lias. 



