24 



"setose", but in C. egrcgia a number of long and strong spines and numerous small spines 

 but no setee are found. 



II. Family Mysid.e Dana. 



A synopsis of the subdivisions of this family is given above. Six subfamilies are 

 enumerated, and all excepting the Mysidellinae are represented in the "Siboga" collection. 



Subfamily I. Boreomysinse Holt & Tatt. 



The essential characters of this subfamily are put together in the synopsis on p. n. 

 Only a single genus, Boreomysis G. O. Sars, is known, as Arctomysis Czern. is a still-born 

 genus founded on a minor error in Kröyer's description of Mysis arctica Kr. 



Boreomysis G. O. Sars. 



A detailed diagnosis of this genus is found in G. O. Sars: Monogr. Norges Mys. III, p. 8 — 9. 



A good number of species were established by various authors : B. arctica Kr., B. nobihs 

 G. O. S., B. trideus G. O. S., B. mcgalops G. O. S., B. obtusata G. O. S., B. microps G. O. S. 

 (= siibpellucida H. J. H.), B. rostrata Illig, B. semicoeca H. J. H., B. scypJwps G. O. S. and 

 B. distingiienda H. J. H. An eleventh species, B. californicn Ortm., seems to be insufficiently 

 described for certain recognition. The "Siboga" material contains some few specimens belonging 

 to three species, all new to science. 



Key to the Species from the "Siboga". 



A. Most of the marginal spines along the distal half of the telson moderately 



large and subequal in length, with very few small spines intermingled. . B. plcbcja n. sp. 



B. The large majority of marginal spines along the distal half of the telson 

 small, and larger spines distributed with nearly regular intervals between 

 the small ones. 



a. Outer margin of the exopod of the uropods with a couple of spines 



considerably longer from the base than the exopod is broad. . . . B. Sibogcc n. sp. 



b. Outer margin of the exopod of the uropods apparently without spines 

 at the distal end of the naked part which is very short, considerably 



shorter than the breadth of the exopod B. incrmis n. sp. 



9. Boreomysis plcbcja n. sp. PI. II, figs. ia — 2d. 



Stat. 143. August 7. Lat. I°4'.5 S., long. I27°52'.6E. 1454111. HENSEN vertical net, from 

 1000 m. depth to surface. 1 immature specimen. 



Description. — Frontal plate considerably produced, with the margins feebly convex, 



