NO. 1 SOOT-RYEN : THE FAMILY MYTILIDAE 33 



Aulacomya is a distinct group. The outer form of the species is like 

 other mytiliform species and is quite variable. Usually there are strong 

 radiating striae over most of the surface, but sometimes, especially in 

 specimens from more northern localities, the striae may be very indis- 

 tinct. . . . The hinge consists of a broadly folded and turned up toothlike 

 lunule in the left valve, vi^ith a corresponding depression in the right one. 

 The nymphae are strong anteriorly and the resilial ridge compact. The 

 anterior adductor is always distinct in small specimens but often obsolete 

 or absent in larger ones (ater). The anterior retractor is elongate, be- 

 hind the umbones ; the posterior retractors are broadly united with the 

 adductor. The posterior part of the mantle is furnished with tentacles. 



This genus comprises three species occurring on both sides of South 

 America, South Africa, Kerguelen Island, and New Zealand. 



Aulacomya ater (Molina) 1782 

 Plate 1, fig. 6; text-figs. 17-18 



Mytilus ater Molina, Saggio sulla Storia Naturale del Chili, 1782, p. 202. 

 Syn.: Mytilus magellanicus Chemnitz 1785 pro parte, Lamarck 1819, 

 non Roding 1798. 



Mytilus bidens Dillwyn 1817, non Linne 1767. 



Mytilus decussatus Lamarck 1819. 



Mytilus crenatus Lamarck 1819. 



Mytilus americanus Orbigny 1846. 



Mytilus pyriformis Gould 1850. 



Mytilus orbignyanus Hupe 1854. 

 Holotype: ? 



Type loc: Strait of Magellan. 



Remarks: Chemnitz (1785, pp. 162-165), who introduced the name 

 Mytilus magellanicus on his PI. 83, figs. 742-743, for what undoubtedly 

 must be this species, has confounded it with Mytilus exustus Linne. Mo- 

 lina (1782) mentions the large and the small Magellanic mussel as dif- 

 ferent from ater, followed by Roding (1798), who used the name Myt- 

 ilus magellanicus for Chemnitz' fig. 738 (PI. 83), which is Perna perna 

 (hinne) = Mytilus elongatus Chemnitz 1785. Molina (1782) has given 

 a short but sufficient description of his ater: "Mytilus testa sulcata, 

 postice squamosa," and says that it grows nearly as large as Mytilus 

 chorus and is like a Pinna with an obscure blue color. 



There have been many different views as to what Molina's ater really 

 is. Dall (1909) mentions ater as a separate species resembling Mytilus 

 edulis, but Lamy (1936) considers it to belong to Mytilus americanus 



