160 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



very much after the Acanthinula pattern, so that, althougli these two 

 are distinct enough as types, yet the intermediate forms are found. 



I have figured the Punctum radula as possessing no external unci. 

 It is, however, possible to find at the extreme margin in some 

 specimens one or two rows whicli forsake the oblique direction above 

 described, and appear to have wider basal plates bearing pectinations. 

 Pectinated externals are quite commonly found in the embryonic 

 radulse of more highly developed forms ; they may be seen, for 

 example, in the embryonic radula of Agriolimax Icevis ; thus one 

 may be sure that the aculeate external is a later development. 



PrRAMiDULA EUPESTRis lias a radula which is superficially very 

 much like that of tlie young Ilelicigona lapicida. The cones are low 

 and fairly uniform in length ; the external basal plates are long and 

 narrow ; there is even an indication of the bifid external mesocone so 

 characteristic of the larger Helices. Also the radula itself is (as in 

 lapicida) rather abruptly divided into a central and two pleural 

 regions ; consequently it is ratlier difficult to make it lie flat on 

 a microscope slide. The radulae of Punctum and Orthalicus can be 

 spread out quite easily, althougli they are very broad relatively 

 to the size of the head. 





^1 



The rounding of tlie cones in the central region of this radula is 

 perhaps due in some waj^ to the habitat of the species. They are not 

 rubbed down to this shape ; if a different view be taken of them they 

 may even appear lanceolate, as in the second row shown in the figure. 

 This is true of lapicida also. A view of the entire radula shows the 

 aspect of rounded cones as normal, the lanceolate appearance being 

 seen in displaced rows. 



In the larger Helices the oldest and most anterior part of the radula 

 is found to taper to a point, so that if the specimen is entire the first 

 row consists of one central uncus alone, or one central and an admedian 

 on each side. If great care be taken to dissect them out, one may 

 occasionally find one or two surviving pectinate unci beside these. 

 Now and then (especially in Th. cantiana) one may find a regular 

 pectinated row external to the normal externals on one or both sides 

 of the radula throughout its length. In the small species which 

 normally have pectinate externals in the adult stage there is little or 

 no tapering of the anterior end; the first row may contain as many 

 unci as the last. Tliis is the case with P. rupestris, and therefore 

 I think it is rightly placed with the Pupiforra Helices, though at the 

 same time I regard it as a very specialized form. 



Our last species is Pteamidula rotund ata. This certainly does not 

 belong to the pectinate group. The serrations upon its externals are 

 very regular and unlike those of any otlier Pritish Helicid. The 



