76 GASTROPODA. [Aspidobranr.hia. 



KEY TO GENERA. 



a. Shell very large, solid, opaque, not iridescent 



(Kermadeo Islands) . . . . . . PATELLA (ANCISTROMESUS). 



da. Shell smaller, solid, interior iridescent or satiny. 

 b. Branchial cordon complete, interior with 



a metallic lustre . . . . . . NACELLA (PATINIGERA). 



66. Branchial cordon interrupted in front, 

 inner layer subtranslucent, more or 

 less iridescent . . . . . . HELCIONISCUS. 



Subfam. 1. NACELLINyE. 

 Developed lateral teeth, but 2 on each side, of which 1 is anterior. 



Genus 1. NACELLA, Schumacher, 1817. 



Nacella, Schumacher, Essai d'un nouv. Syst., 1817, 179. Type : Patella 

 mytilina, Helb. Nacella, Dall. Arner. Journ. Conch., vi. 274; not Nacella 

 of Carpenter, Sars, et al. 



The gill-cordon is continuous ; the foot is encircled by a scalloped 

 epipodial ridge, interrupted in front. One inner lateral tooth on 

 each side anterior ; central tooth none, or rudimentary. The shell 

 has the apex subcentral or anterior, and is characterized by a pecu- 

 liarly metallic texture, having the central area of the interior generally 

 of a red-bronze colour. 



Cape Horn was evidently the birthplace of Nacella and Patinigera. 

 Thence they have been distributed eastward to the Falkland, New 

 Georgia, and Kerguelen Islands by the eastward-sweeping antarctic 

 current carrying them upon seaweeds. (Pilsbry.) 



KEY TO SPECIES. 



a. Shell elevated conical, 20-25 distant radiate ribs, with 1-3 inter- 

 vening striae . . . . . . . . . . . . illuminata. 



aa. Shell compressly raised, 30-60 radiate riblets, crossed by close 



undulating ridges . . . . . . . . . . fuegiensis. 



Sect. PATINIGERA, Dall. 1905. 



Patinella, Dall, Amer. Journ. Conch., vi, 1871, 272 (preoccupied). Patinigera t 

 Dall, "The Nautilus," xviii, 1905. 113. Type: Patella magdlanica, 

 Gmel. 



1. Nacella fuegiensis, Reeve, 1855. Plate 7, fig. 7. 



Patella fuegiensis, Reeve, Conch. Icon., Patella, f. 73. Patella (Patinella) 

 fuegiensis, E. A. Smith, Trans. Roy. Soc.. 1879, 14, pi. 9, f. 14, 14a ; 

 Rochebrune and Mabille, Miss. Sci. du Cap Horn, 95 ; Filhol. Miss. I.C., 

 529 ; Deutsche Tiefsee Exp. l> Valdivia," A, 72. Nacella fuegiensis, 

 Reeve: Pilsbry, Man. Conch. (1), xiii. 121, pi. 49, f. 28-31 ; Surer, P. 

 Mai. S., vi, 353 ; Subantarct. Islds. N.Zeal.. i, <>. 



Shell oval, rather thin, semitransparent, compressly raised. Sculp- 

 ture consists of 30 to 60 ribs, densely crossed by beautiful raised and 

 undulating concentric ridges. Colour brown or greenish, more or 



