168 Proceedings of the Royal Physical Society. 



lieve to be identical with the above, lead me to believe them 

 distinct from Naticopsis, and for these reasons — the inner lip 

 is not reflected to the same extent as in JVaticopsis. In no 

 single instance have I seen it plaited, or striated, and the re- 

 markably straight, continuous, and direct course it pursues is 

 so very unlike the callous, reflecting, corresponding structure in 

 M'Coy's genus, that I do not see how our little shell could be 

 considered as congeneric with its species. The umbilicus being 

 a debatable point, it is perhaps better at present not to refer 

 to it as a means of comparison. One point of resemblance 

 exists with Naticopsis, in the stronger form of the fine striae 

 immediately around the suture, and also with some species of 

 the genus, in the deep channelling of the latter. 



In washing the shale in which P. Scotohurdigalensis occurs, 

 Mr Bennie endeavoured to obtain traces of opercula, but I 

 am sorry to say without success. The acquisition of this 

 structure would go far towards proving, or on the other hand 

 disproving, the view of its affinity now advocated. 



Another point which presents itself is — does the condition 

 under which P. Scotohurdigalensis is met with at Eaw Camps 

 and Craigkelly represent the mature or immature form ? I 

 think the well-defined mouth, thickened outer, and reflected 

 inner lip can point only to one conclusion — that the shells 

 are mature. This is, in a great measure, borne out by the 

 great quantity in which the shell is found, and in no case at 

 these localities exceeding a certain size, although in itself 

 very small. 



From Strophostyhcs (Hall), the little shells I have termed 

 Platyostomella, are distinguished at once by the reflected lip, 

 both inner and outer, and by the absence of twisting or 

 spiral-grooving on the former. The general form is, to some 

 extent, similar, as, indeed, it is in the whole of this group, 

 Naticopsis, Strophostylns, and Platyostoma. Again, if an 

 umbilicus exists in Platyostomella, there is still here a furthe^ 

 departure from Strophostylus, as Professor Hall distinctly say^ 

 there is none in the latter. 



The resemblance to Platyostoma, on the other hand, is 

 very marked, especially in the form of the mouth, reflected or 

 thickened lips in particular, and the almost at right-angles- 



