74 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



At least two of these species live in a test of Ascidia (M. marmoratus 

 and M. lebourae). These species certainly should be removed from the 

 genus Musculus and placed in a separate genus. Swainson, 1840, p. 385, 

 described Lanistes (as of Humphreys) w^ith one species, Mytilus discors 

 (Enc. Meth. 204, f. 5), which is Musculus impactus (Hermann) 1782. 

 Unfortunately Lanistes is preoccupied by Montfort 1810. Gray, 1847, 

 gave a new name Lanistirm to replace Lanistes Swainson, and this name 

 seems to be valid for the species of the Musculus impactus type. But 

 Gray in 1843 had used the genus Modiolarca for impacta and if this is 

 not a misprint for Modiolaria, it antedates Lanistina by four years. Until 

 this question is solved, it seems best to use Lanistina Gray 1847. Whether 

 species belonging to Lanistina occur on the west coast of America is not 

 proved, as the record of Musculus marmoratus (Forbes) from Puget 

 Sound seems doubtful. 



Many species and varieties of Musculus are recorded and described 

 from the Arctic Seas, the Bering Sea, or to the north of California, but 

 two species only are found along the coasts of California. Both seem to 

 be rare. M. senhousei (Benson) is introduced. 

 Key to the west American species : 



1. Shell thin, green colored with 



faint radiating striae posteriorly senhousei (Benson) 



Shell more solid, olive to black- 

 ish with distinct posterior striae 2 



2. Sculpture on the median part of 

 the shell irregularly concentric, 



color olivaceous with silky lustre olivaceus Dall 



Median part of the shell smooth, 



blackish protr actus Dall 



Musculus senhousei (Benson) 1842 



Modiola senhousia Benson, Ann. and Mag. Nat. Hist., vol. 9, 1842, p. 



489. 

 Syn.: Modiola senhausiiKeeve 1857. 



Modiolus senhousei Lamy 1936. 



Brachyodontes senhausi Jukes-Browne 1905. 

 Holotype: British Museum. 

 Type loc: Chusan, China. 



Remarks: This species, generally considered to be a Modiolus, has the 

 characters typical of the genus Musculus, e. g., the anterior retractors 



