160 J. Starliie Gardner — Cretaceous Gasteropoda. 



of one or other of the pre-Cambrian ridges separated the area from 

 the more disturbed sea in which the Yolcanos were active, so that in 

 this way a limestone might continue to form on one side, whilst it 

 was being interrupted on the other, and hence diversities in thick- 

 ness and in the character of the sediment may be shown even within 

 comparatively limited areas. That several of these ridges still existed 

 at the close of the Lower Silurian in the western, or north-western 

 areas in Europe and in North America, there is ample proof to show, 

 whilst in Asia it is probable that a continent of considerable size formed 

 of these rocks was still above water-level at this time. Speaking 

 generally of the conditions during the Cambrian and Lower Silurian 

 epochs, we may say that at first continents of great size occupied 

 the higher latitudes, that these were traversed by mountainous 

 ranges of great height, that the depression took place generally from 

 the latitude of 30*^ northward, though possibly more decidedly along 

 certain lines, as from south-west to north-east in Europe, and from 

 south-east to north-west in North America, that the sediments over 

 each area give indications of shoal conditions at first and of being 

 the result of denudation only, and afterwards of having been heaped 

 up chiefly by marine life, except where volcanic material jointly 

 assisted in forming them. 



[To he continued in our next Number.) 



lY. — On Cretaceous GASTEnoroDA (Scalaeifoem Shells). 



Ey J. Stakkie Gardner, F.G.S, 



{Concluded from the March Number, page 114.) 



THE remaining shells figured on Plate lY. do not belong to the 

 Scalidce, but to families considerably removed. The form next 

 described undoubtedly belongs to the family of A;porrliaidce, the rest 

 are Missoidce. 



In my concluding paper on Aporrhaidce, Geol. Mag. Dec. II. Yol. II. 

 page 394, 1 constituted the species I had described into four genera. 

 I was unable to assign the shell I am about to describe to any of 

 the genera then constituted, and therefore left it undescribed, hoping 

 that time might throw some additional light on its affinities. No 

 additional information, however, has been forthcoming, and no second 

 specimen has been found at Folkestone. Through the kindness of 

 Mr. Jukes-Brown, I have, however, received two specimens from 

 Cambridge; he has also compared my Folkestone specimen with 

 that originally figured by Seeley as Sc. angidaris, and I no longer feel 

 justified in delaying to add this singular form to those I have already 

 made known. The character of the outer lip and last whorl is so 

 peculiar as to preclude this shell from being placed in any one of 

 the genera already formed, and I therefore propose a new sub-genus 

 to receive it — 



Beachystoma, J. S. G. 



Shell turreted, elongated ; whorls ribbed ; last whorl angulated, 

 bicarinated ; outer lip thin and turned slightly inwards, projecting 

 beyond the spiral angle ; mouth angular. 



