NO. 1 SOOT-RYEN : THE FAMILY MYTILIDAE 25 



Genus SEMIMYTILUS new genus 



Diagnosis: Shell mytiliform with nearly terminal umbones; lunule small 

 and circumscribed by a fine line ; anterior margin without teeth, slightly 

 bent outward and usually constricted to form a rounded anterior margin. 

 Anterior adductor present, posterior adductors and retractors continuous, 

 anterior retractor fastened below the ligament behind the umbo, elongate, 

 narrow, separated in the middle; resilial ridge compact. Pallial margin 

 with groups of papillae. 

 Type of genus: Mytilus algosus Gould 1850. 



This genus differs from Mytilus s. s. and Perna by the compact resilial 

 ridge, from Choromytilus by the presence of an anterior adductor, and 

 from all by the lack of teeth on the lunular margin. The fine incised line 

 which circumscribes the lunule and constricts the anterior margin is of 

 the same type as the two or more lines found on the lunule of species of 

 the related genera and there forming teeth on the anterior margin. 



So far as is known, Mytilus algosus is the only species which is refer- 

 able to this group. There are some small Pacific species which perhaps 

 are closely related, but a thorough study of preserved specimens is neces- 

 sary before any other species can be referred to Semimytilus. 



If no other species should be referable to SemimytiluSj this group is 

 confined to the west coast of South America. 



Semimytilus algosus (Gould) 1850 

 Plate 4, fig. 17; text-figs. 8, 9, 14, 15, 16 



Mytilus algosus Gould, Proc. Boston Soc. Nat, Hist., vol. 3, 1850, p. 

 344; United States Exploring Expedition, vol. 12, 1852, p. 450, Atlas, 

 1856, PI. 41, figs. 566, 566a. 

 Syn.: Mytilus dactyliformis Hupe 1854. 



Mytilus splendens Dunker 1856, non Reeve 1857. 



Mytilus cuneiformis Reeve 1857, non Hanley 1843. 



Mytilus angustanus Reeve 1857 (Clessin 1889), non Lamarck 



1819. 

 Mytilus patagonicus Clessin 1889, non Orbigny 1846. 

 Mytilus similis Clessin 1889. 

 Modiolus nonuranus Pilsbry and Olsson 1935. 

 Holotype: U. S. National Museum? 

 Type loc: Fiji Islands (!) wrong locality. Valparaiso, Chile, is here 



designated as the type locality. 

 Remarks: Unfortunately Gould gave "Feejee Islands" as the locality 

 where this species was obtained by the Exploring Expedition. Several 



