80 PATELLA. 



Section NACELLA s. str. Gills very small in front. Shell 

 oblong, thin, the apex curved forward, near or at the an- 

 terior extremity of the shell. Type P. mytilina. 



Section PATINELLA Dall, 1871. Gills equally developed all 

 around. Shell solid, colored, ribbed, the apex subcentral 

 or anterior. Type P. magellanica. 



Subgenus HELCIONISCUS Dall, 1871. 



Branchial cordon interrupted ; sides of the foot smooth, lacking 

 epipodial processes. Ons inner lateral tooth on each side, anterior. 

 Shell solid, having the apex subcentral or subanterior, inner layer 

 subtranslucent, more or less iridescent or satiny. Type H. variegatus 

 Rve. 



Resembles Patinella in texture of shell and dentition, but lacks 

 an epipodial ridge, in the latter respect resembling Patella. It 

 differs from both in having the branchial cordon interrupted in 

 front. 



Genus PATELLA L., 1758. 



Patella L., p. Syst. Nat. x, p. 780 (in part). Eruca TORNEFORT. 

 Patellites WALCH. Patellaria LLHWYD. ? Goniclis RAF. olim. 

 Patellus MONTFORT. 



Subgenus PATELLA (restricted.) 



The subgenus is here considered to= Patella^ Ancistromesus of 

 Dr. Dalls's arrangement. It is one of the best-defined groups of the 

 family, being characterized by (1) the continuous branchial cordon, 

 (2) smooth sides of the foot, having no epipodial ridge or processes, 

 and (3) having a peculiarity of the radula found in none of the 

 other groups except Helcion-\- Patina ; viz., the two inner lateral 

 teeth on each side are unicuspid and situated in front of the third 

 laterals, which are larger and have several (generally three) cusps. 

 This disposition is easily understood by reference to pi. 52, fig. 1 

 representing the odontophore of Patella vulgata. In some species a 

 central or rhachidian tooth is developed, and when this is the case 

 it is placed on the same level with the inner laterals. See under 

 section Ancistromesus. 



A reference to the synopsis of groups on page 79 shows that the 

 subgenus consists of three sections, of which the first is 



