160 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 109 



was found nestled in Barentsia gorbunovi at 341 feet; about 30 (up to 

 9 mm.) were attached to B. gorbunovi at 438 feet; and a small 

 individual was found nestled in the tunic of Boltenia echinata. 



Most of the larger individuals were encased in a capsule of byssal 

 threads, but no individual less than 13.5 mm. long was found in a 

 byssal capsule. In one encapsuled specimen (20.4 by 12.6 by 8.1 

 mm.) from Eluitkak Pass, stolons of hydroids were interlaced through 

 the byssal threads and among this netv/ork were nestled a Hiatella 

 arctica 6.6 mm. long, an annelid worm about 7 mm. long, and 2 

 sipunculids, Golfingia margaritacea, about 5 and 7 mm. long. One 

 specimen 22.5 mm. long that was taken from 328 feet was in a capsule 

 that was covered with a colony of the bryozoan Dendrobeania murray- 

 ana, which, in turn, provided space for colonies of 2 other bryozoans, 

 2 species of h^^droids, some sponges, foraminifers, and a Hiatella 

 arctica 5.8 mm. long. 



Another specimen 22.4 mm. long from 328 feet (Sept. 1, 1949) 

 was encased in a byssal net to which were attached colonies of a 

 brj'^ozoan, and attached to this mass was a Musculus discors var. 

 laevigatus 2.2 mm. long and another smaller one. A large encapsuled 

 individual was taken at 341 feet. The sm.allest encapsuled individual 

 (13.5 mm.) taken at 453 feet, was attached to the stalk of the tunicate 

 Boltenia ovifera. Two others (15 and 17.5 mm. long) from 453 feet 

 were in capsules to which were attached colonies of Barentsia gor- 

 bunovi and Eucratea loricata with their attached fauna. Tv/o (19.5 

 and 21 mm.) from 477 feet were in capsules matted with nematodes, 

 and tiny sponges and small colonies of Eucretea loricata were attached 

 to one of the cases. Only a portion of these capsules was opened, 

 but no eggs were found in those examined. 



Other material examined: About 50 specimens from localities 

 ranging from Bernard Harbor, Northwest Territories, and Ic}^ Cape, 

 Alaska, south and east to the Aleutians and Puget Sound; and over 

 75 specimens from localities ranging from the Melville Peninsula and 

 Greenland to Connecticut, and from Spitzbergen and Norway. 

 (Two from between Bristol Bay and the Pribilofs and one from Sitka 

 Harbor were in byssal capsules.) 



Discussion: There has been considerable difference of opinion 

 regarding this species and its varieties. Jensen (1912) has shown that 

 M. laevigatus Gray and M. substriatus Gray are not distinct species. 

 The former is a variety of M. discors (see Jensen, 1912, pi. 3, figs. 

 6a-b) in which the posterior striations are lackmg (Jensen, 1912, pi. 3, 

 figs. 4a-b) and M. substriatus is merely a form of var. laevigatus in 

 which the posterior striations are visible but faint (Jensen, 1912, pi. 3, 

 figs. 5a-c). In true M. discors the posterior striations are distinct, 

 as in M. corrugatus (Jensen, 1912, pi. 3, figs. 7a-d), but in M. discors 



