30 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



Perna perna (Linne) 1758 

 Text-fig. 6 



Mya perna Linne, Systema Naturae, ed. 10, 1758, p. 671. 

 Syn.: Mytilus elongatus Chemnitz 1785. 



Perna magellanica Retzius 1788. 



Mytilus magellanicus Roding 1798. 

 Holotype: ? 



Type loc: Strait of Magellan. 



Remarks: Linne described this species as a Mya. His short description is 

 followed by a reference to "Argenv. conch, t. 25, f. N" and the habitat is 

 "in freto Magellanico." Argenville, PI. 25, fig. N, represents an elongate 

 mytilid and on p. 331 sub. fig. N, he says: "La Moule qu'on voit a la 

 lettre N, est d'une tres beau violet mele de Pourpre & d'Agathe, c'est la 

 grand Moule de Magellan." There is no doubt the Linnean name perna 

 has to be used for the South American species. Ihering (1900) uses 

 Mytilus perna Linne for the Brazilian species (Mytilus achatinus Lam- 

 arck, Lamy 1936), which perhaps may be conspecific with the Magel- 

 lanian form. In fact, Lamy (1936) reports M. achatinus from the Strait 

 of Magellan and M. elongatus Chemnitz from Brazil. Carcelles (1950, 

 1951) does not mention this species in his lists. 

 Occurrence: No information available. 



Distribution: Strait of Magellan north to ? on the Atlantic coast of 

 South America. 



Genus GHOROMYTILUS Soot-Ryen 1952 



Choromytilus Soot-Ryen, Rev. Soc. Malacolog. "Carlos de la Torre," 



vol. 8, no. 3, 1952, p. 121. 

 Type of genus: Mytilus chorus Molina 1782 (orig.). 

 Remarks: This group was described mainly because the resilial ridge is 

 compact and this makes it easily separable from Perna. There are, how- 

 ever, other characters which separate these species from related groups. 

 The posterior byssus and foot retractors are continuous though some- 

 times only narrowly connected ; the anterior retractor is strong, very 

 strong and elongated in C. palHopunctatus, and fastened to the valves 

 approximately below the middle of the ligament. The tentacles on the 

 posterior mantle margin are large and branched, and the valves are usu- 

 ally punctate inside the ventral half. The anterior adductor, wanting in 

 larger specimens, may be seen in young specimens. The byssus is very 

 strong, branching from a central stem. The lunule is bent inwards, form- 

 ing one central tooth in the right valve corresponding to a groove in the 

 left valve. 



