40 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



H. adamsiana is so like some of the forms of Septifer bifurcatus that 

 the shells have to be opened to make the identification quite certain. 

 Occurrence: Intertidal on rocky shores. 



Distribution: Ecuador to Santa Barbara, California, including the Gulf 

 of California and the Galapagos Islands. 



Hormomya granulata (Hanley) 1843 

 Plate 3, fig. 12; text-fig. 26 



Mytilus granulatus Hanley, Catalogue of Recent Bivalve Shells, 1843, p. 



246, PI. 24, fig. 33. 

 Holotype: British museum. 

 Type loc: South America. 



Remarks: This is the typical South American Hormomya living along 

 rocky coasts. The color is yellowish-brown and the radiating ribs, which 

 are of approximately the same width as the interspaces, are furnished with 

 round granules, easily seen in side view. Large specimens are usually more 

 inflated, with the anterior part strongly curved, giving the shells an odd 

 appearance. The hinge is variable, but the right valve usually has three, 

 the left valve two, stronger teeth. The posterior part of the mantle is 

 furnished with papillae and the septum has a rather long median flap. 

 Occurrence: Intertidal, fastened to rocks. 

 Distribution: Lobos, Peru, to southern Chile. 



Genus SEPTIFER Recluz 1848 



Septifer Recluz, Revue ZooL, 1848, p. 275. 



Type of genus: Mytilus bilocularis Linne 1758 (subsequent designation 



byStoliczka 1871). 

 Remarks: Species of this genus generally are very like Hormomya species, 

 but they are easily separated by the anteriorly placed deck or septum for 

 the anterior adductor. For some species, such as the California Septifer 

 bifurcatus, it is necessary to open the shells before a determination can be 

 made. 



The outer form, sculpture, marginal crenulations, and hinge are very 

 like those of Hormomya, and the mantle is armed with tentacles or 

 papillae like those found in Hormomya species. The septum seems to 

 grow out in the same way as the thick, elevated adductor scar in Hor- 

 momya or BrachidonteSj since the anterior adductor becomes very narrow 

 in shells with the ventral side flattened. The posterior adductor embraces 

 the retractors dorsally, so these scars are different from Hormomya. 



Species of Septifer are recorded from the Cretaceous. The recent spe- 



