162 W. IT. EudUston—On the Yorhhire Oolites. 



has sncceeiled in depicting this shell with great skill and fidelity. 

 It must not be supposed that the spiral ornamentation is absent, bnt 

 it is overpowered by the radial ornamentation. The keel is slightly 

 imbricated, and doubtless contained the slit-band, though we must 

 . partly rely upon inference in arriving at this conclusion. 



Another specimen. — From the soft reddish marly grit with grey 

 ova of the Kelloway Eock (zone 5), Scarborough or Hackness. 

 Bean Collection, British Museum, This one represents the more 

 ordinary' condition of the fossil, and would at once be recognized 

 as PI. depressa, Phil. Not figured. 



The four inner (posterior) whorls greatly resemble those of the 

 preceding specimen ; the ornamentation is coarser, and the spiral 

 system more obvious. The development of a discoidal body- whorl, 

 which nearly doubles the width of the shell, constitutes the chief 

 difference. Since this body-whorl is in a " half cast " condition, it 

 is difficult to say how far the angular shape of the whorls of the 

 spire is retained ; but judging from some remains of the outer shell, 

 it would seem as though the smooth outline of the body- whorl (see 

 figure in G. Y. pi. vi. 12), does not in any way represent the ex- 

 ternal form originally possessed by the specimen. Umbilicus wide 

 and deep. 



Another specimen. — From the Oxford Clay (zone 6), Scarborough. 

 York Museum. Fig. 1. 



This has been compressed till it is not much thicker than a crown 

 piece ; but the fineness of the ornamentation, and the general aspect 

 of the shell serve to connect it with Leckenby's PI. striata. An 

 inspection of the figure will do more in this case than any further 

 attempt at description. 



Belations and Distribution. — Although this species, in common 

 with the one last described (PI. granulata, Lycett, non Sow.), is a 

 member of the granulata-gYOw\), it differs from the general average 

 of Inferior Oolite fossils referable to Sowerby's species in a direction 

 almost opposite to that of Lycett. Instead of having a higher spire 

 than the true PI. granvlata, the shell is extremely depressed, the 

 whorls being very angular and tabulate. It is considerably ex- 

 cavated, and thus agrees better with the generality of Inferior Oolite 

 specimens belonging to the granulata-^roup. On the other hand, 

 the ornamentation is much finer, and this is so marked in Leckenby's 

 PL striata, that subsequently his species may come to be regarded as 

 a variety of PL depressa. 



Nothing can be more difficult than to trace a particular member of 

 the gramdata-group through a cloud of synonyms. The Inferior 

 Oolite fossil to which PL depressa bears the most resemblance is 

 PL palemon, D'Orb., though more in shape than in ornamentation. 

 Quoted by Brauns under the name of PL granulata, Sow., from the 

 equivalents of the Cornbrash and Kelloway Eock of N.W. Germany. 

 In Yorkshire PL depressa is only known from the Kelloway Eock 

 and Lower " Oxford Clay," in the latter of which it is rare. 



