798 PROF. G. O. BOUR>fE ON THE 



anterioi' extremities bearing denticulations. Thus, there is a 

 consiclei'able difference between Etitrochatella and Helicina, bnt the 

 gap is bridged over by Trochatella clirysochasma, in which, accord- 

 ing to Trosche], the lateral tooth is pileiform, but with an oblique 

 anterior border beaiing from 7 to 9 denticulations, and whereas 

 the proximal marginal teeth are simply pointed as in Etitrochatella, 

 the more distal marginals bear denticulations, increasing from one 

 to four in number. I have shown that anatomically Eutrochatella 

 bears the closest resemblance to Alcadia, differing only in the 

 arrangement of the coils of tlie intestine. 



The genus Alcadia is characterized by a notch separating the 

 peristome of the shell from the columella. It is stated (Fischer, 

 ' Manuel de Conchyliologie,' p. 795) that the operculum has a 

 dentiform process: I can only say that I cannot find a trace of 

 any such structure in J., palliata and A. hollandi. In all other 

 respects Alcadia is similar to the point of identity to Helicina. 

 Troschel declares that the only recognizable diff'erence between the 

 radulas of Alcadia and Helicina is in the form of the median tooth, 

 a character of very little value, for, as I shall show, the shape of 

 this tooth varies from species to species. But Troschel's figure of 

 the radula of Alcadia is not very exact. I have given in PI. XL. 

 fig. 58, atof, large scale drawings of the teeth of A. hollcondi :, 

 those of A. palliata differ only in minute particulars. Oompaiing 

 these Avith the drawings of the radulae of Litcidella, Fala^ohelici'iia, 

 Orobophana, and Aphanocoiiia (Pis. XL.- XLII. figs. 59-65), it 

 will be seen that the first admedian tooth of Alcadia has a 

 characteristic shape, being subquadrangular in outline, with its 

 anterior outer angle produced into a knob on which are borne 

 four blunt denticulations. The large lateral has a short stalk, 

 hardly projecting behind the oiigin of the aliform plate : the 

 latter is large, expanded, bearing seven stout but blunt teeth on 

 its recurved anterior margin. The ai'ticular excavation is very 

 shallow : the external process long and pointed. 



Of the other radulte figiued, those of Falwoheliciva (PI. XLI. 

 fig. 60) and Aphanoconia (Pis. XLI. k XLII. figs. 62-65) bear the 

 closest resemblance to Alcadia. Both these genera were included 

 in Helicina Lamarck, and have only recently been separated by 

 Wagner. In them the lateral teeth have the same general shape 

 as in Alcadia, but the stalk is longer, the aliform plate less 

 expanded, the denticulations on its anterior border vary in size, 

 shape, and number. The first admedian tooth is very similar in 

 the two genera, and differs from that of Alcadia. The median 

 tooth is very variable in size and shape. The similarity of the 

 radulse of Pcolceohelicina and Aphanoconia is remarkable, and leads 

 one to doubt whether Wagner is justified in placing these forms 

 in different genera. On the other hand, Oroho]jhana (PI. XLI. 

 fig. 61) is distinct : its lateral tooth is that of Palmoheliciva, but 

 the first admedian is relatively large, acutely triangular, its 

 anterior border thickened but without denticulations ; it is 

 feebly coi-neous and nearly transparent, suggesting that it is in 



