J. Starkie Gardner — On Cretaceous Aporrhdidce. 393 



Greensand, Chloritic-marl, and Chalk, in cabinets which I have not 

 yet seen, and I should be obliged to any one who would inform me 

 of them." 



I have made an endeavour to supply this want of information, and 

 in reply to the hope I expressed, that my attention might be directed 

 to collections I had not seen, I had kindly sent to me specimens by 

 Mr. C. J. Meyer, Mr. Jukes Brown, and Mr. E. B. Tawney. I have 

 also been able to see the Cunnington collection, which a month or two 

 ago was purchased by the Government, and lodged in the British and 

 Jermyn Street Museums. Instead of confining myself, as I at first 

 intended, to the Gault of Folkestone, I can also now include the 

 Neocomian and the Grey Chalk, from which I have recently collected 

 specimens myself. The result of the additional information I have 

 thus gained is that I am now in the position to offer a different 

 grouping from that which I have already suggested. 



My proposed grouping now is given on page 394. 



On Dimoephosoma. 



When I first described the series of specimens of Aporrhais 

 calcarata, Sby., I, in common with others, was led to consider them 

 local varieties, which were the result of local conditions of sea. 

 This is a natural inference at first sight ; for while there is so great a 

 similarity in the apical whorls, the invariably bicarinated body- 

 whorl, the simple wing, and the more or less ribbed spire, which are 

 common to all the specimens, it is not so apparent that the minor 

 characters are constant. 



A suggestion of Mr. Meyer's has led me to carefully inspect a 

 large number of specimens, many of which he has kindly lent me 

 himself. My information has also been extended by my recently 

 finding three distinct species in the Chalk near Dover. Besides the 

 easily recognizable constant characters mentioned above, the characters 

 which I regarded as varietal I now find to be also constant through- 

 out all the large number I have seen, and I therefore now consider 

 them to have specific value. These characters are given seriatim 

 further on. 



Still more important is the suggestion I am about to make that 

 this group ought to be recognized as constituting a separate genus, 

 possibly indeed it may have to be regarded as a separate family. I 

 suggest this on the ground of what I suppose to be their mode of 

 growth. 



Mode of Growth. — All specimens of the fry are seen to be keeled 

 and without transverse ribs : with the third or fourth whorl a wing 

 process is developed, and in most cases these whorls become ribbed. 

 This early development of the wing and its persistence throughout 

 the whole growth of the shell is a very unusual character. In the 

 families of Strombidce and Aporrhaidce the wing is produced only 

 after the shell has attained its adult stage, at which time the growth 

 of the shell is confined to forming and thickening the wing in suc- 

 cessive layers, instead of increasing the number of whorls. 



