NO. 1 SOOT-RYEN : THE FAMILY MYTILIDAE 45 



Hormomya adamsiana. There appears always to be a smooth or obsoletely 

 sculptured part behind the lunule; and the dorsal sculpture sometimes 

 consists of distinct, but not exceptionally coarse, radiating ribs. The sculp- 

 ture usually is fine and sometimes completely absent. The color varies 

 from dark purple or brown dorsally to yellowish, white, or greenish-olive 

 ventrally. The hinge is furnished with one to three, usually two, dark 

 purplish larger teeth. Maximal length of specimens at hand is 13.2 mm. 

 Occurrence: Intertidal among algae. 



Distribution: From the northern part of the Gulf of California and 

 Punta Rosarita, Baja California, to Ecuador. 



Brachidontes purpuratus (Lamarck) 1819 

 Plate 4, fig. 18 ; text-fig. 30 



Modiola purpurata Lamarck, Animaux sans vertebres, vol. 6, part 1, 



1819, p. 113. 

 Syn.: fMytilus ovalis Lamarck 1819. 

 fMytilus exilis Philippi 1847. 

 fMytilus exaratus Philippi 1847. 

 Mytilus bifurcatus Dautzenberg 1896. 

 Holotype: lost. 

 Type loc: ? 



Remarks: This species is extremely variable in form, sculpture, and color. 

 Usually larger specimens are more or less worn, white on the beaks and 

 on the anteroventral part, otherwise purplish with traces of the blackish 

 periostracum. Large specimens of 40 mm in length are not uncommon. 

 The hinge consists of several crenulations of nearly equal size and thus 

 fits the description of Brachidontes much better than that of what was 

 considered to be the type species. 



The papillae on the posterior part of the mantle are puzzling, as they 

 are sometimes quite distinct but usually seem to be completely absent. 

 The retractor scars are often separated into several parts, usually six for 

 the posterior muscles and two for the anterior ones. The anterior adduc- 

 tor scar is often very thick and raised above the main interior surface, 

 simulating a "septum" to some degree. The marginal crenulations vary a 

 great deal, but there are always distinct tooth-like crenulations behind 

 the ligament. 



Occurrence: Intertidal on rocky shores. 



Distribution: Ecuador south to the Strait of Magellan. Atlantic north to 

 Santa Cruz, Argentina. 



