172 APPENDIX-PATELLID.E. 



opinion are inevitable, and it must be left to the zoologists of the 

 future to sift these things down to a just, convenient and uniform 

 usage. It should be noted, however, that most of the above " genera " 

 are founded upon the degrees of development of a single organ. 



I have copied on pi. 52, fig. 6, Thiele's figure of the radula of 

 Patellidea granularis. On pi. 74, fig. 1, dentition of Patellona grana- 

 tina. On pi. 52, fig. 7, the dentition of Olana cochlear. On pi. 74, 

 fig. 2, that of Cymbula compressa. On pi. 52, fig. 8, that of Patellastra 

 lusitanica. On pi. 52, fig. 5, that of Patella aspera. On pi. 52, fig. 

 9, that of Patellopsis sp., a Cape species of which the shell is unknown. 



PI. 52, fig. 4, represents the dentition of Helcion pectinatus. PI. 52, 

 fig. 3, that of Patinastra pruinosa. PI. 52, fig. 2, the dentition of 

 Patina pellucida. 



On pi. 74, fig. 3, the dentition of Nacella vitrea is figured. PI. 74, 

 fig. 4, represent that of N. mytilina. PI. 74, fig. 5, that of Patinella 

 venosa. PI. 74, figs. 7, 8, that of P. faegiensis. 



PL 74, fig. 6, represents the dentition of Helcioniscus capensis. 



It is likely that naturalists of all schools could agree upon some 

 such arrangement of this family as the following: 



REVISED CLASSIFICATION OF THE PATELLID^E. 



Family Patellidce. 



I. Subfamily PATELLIN^. Lateral teeth of the radula three on 

 each side, two of them anterior. 



1. Genus Patella L. Branchial cordon complete ; apex of 



shell near the center. 



2. Genus Helcion Montf. Branchial cordon interrupted in 



front ; apex of the shell anterior. 



II. Subfamily NACELLIN^E. Developed lateral teeth but two on 

 each side, of which one is anterior. 



3. Genus Nacella Schum. An epipodial ridge developed 



upon thesides of the foot; branchial cordon complete. 



4. Genus Helcioniscus Dall. Sides of foot smooth, with no 



trace of an epipodial ridge. Branchial cordon inter- 

 rupted in front. 



