56 TF. JS. Hudleston — On the YovhsMre Oolites. 



Fig. 8. — Same horizon and collection as the above. 



Lenjjtli (restored) 11 millimetres. 



Width ; 3| „ 



Spiral angle about 22°. 



Whorls nearly flat ; spirals 4, with but slight prominence of the 

 upper row, longitudinals straight. 



As this specimen happens to have no more than 4 spirals, it would 

 do for G. quadrilineatum, Eom., but for the fact that the longitudinal 

 costula3 in Eomer's species are described as being subarcuate, whilst 

 these are certainly very straight. Brauns (Mittl. Jura, p. 171) 

 includes specimens with 5 spirals under this heading, and, if a little 

 more latitude be given, C. quadrilineatum might be made to cover 

 most varieties of the mimcatwn-grou-p from this low horizon. 



Relations and Distribution of the C. muricatum-growp. — Unless we 

 are prepared to make a distinct species out of every variety of this 

 most abundant and widely-spread group of fossil shells, the only 

 alternative method of dealing with the subject at all practicable is 

 to regard the numerous modifications as representing varieties within 

 certain limits, such as those laid down in the general diagnosis. 



In the Leckenby Collection may be seen a number of these forms 

 from the Dogger Sands, nearly every one of which shows some 

 difference. Specimens with 4 (Fig. 8), 5 (Fig. 7), 6 (Fig. 3), spirals 

 occur ; likewise specimens with arcuate longitudinals (Figs. 3 and 7) 

 and straight longitudinals (Fig. 8), though the former are decidedly 

 the most numerous. On the whole, specimens from the Sands run 

 rather larger than do those from the Dogger, the varieties Figs. 7 

 and 8 having been selected simply to illustrate extremes. The most 

 common form in the Sands is exemplified by Fig. 2, though that 

 happens to represent a Dogger specimen. I regard this as the 

 standard or typical form (not necessarily the type) of the group, 

 it having the most resemblance to the well-known Steeple Ashton 

 fossils. All the forms that do not come up to this standard might 

 be regarded by thorough species- makers as distinct. When we 

 ascend into the Dogger itself, the group is less numerous, and the 

 varieties apparently more restricted; but we find the straight-ribbed, 

 flat-whorled sort (Fig. 1) with 4 spirals, in addition to the form 

 (Fig. 2) which I have described as most typical. In the succeeding 

 zones the group is very rare, and is represented by such divergent 

 forms as Figs. 4, 5, and 6 from the Cornbrash, Kelloway Eock and 

 Scarborough Limestone respectively — divergent after making all 

 due allowance for difference of fossilization under different physical 

 conditions. I am not aware of any specimens having been found in 

 the Oxford Clay of Yorkshire, but the form with 4 spirals (identified 

 with C. Russiense, D'Orb., see "Corallian Gasteropoda") is not very 

 iincommon in the Lower Calcareous Grit ; whilst in the Coralline 

 Oolite, especially at Pickering, both forms which occur in the Dogger 

 are again seen, but far more abundantly, especially the 6-spiral form, 

 with curved longitudinals. 



There does not appear to be anj"^ great regularity or plan in these 

 varieties of ornament, so that a trinomial system of nomenclature 



