A REVIEW OF THE MYSIDACEA 213 



most closely allied to A. costata and A. sculpta but differs from both 

 in the absence of any special sculpturing on the sixth abdominal somite 

 other than the simple furrows and ridges. The telson is more like 

 that of A. costata than of A. sculpta. 



ACANTHOMYSIS DYBOWSKII (Dershavin) 

 FlGUBE 89 



Orientomysis dybotvskii Dershavin, 1913, p. 203, figs. 11-15. 

 Acanthomysis dybowskii Ii, 1936b, p. 597, figs. 47-55. 



Occurrence. — Bering Sea region : Albatross station 3239, 1 female ; 

 Petropavlovsk, Kamchatka, Albatross collection, 1906, 25 adult 

 females, breeding ; Chiachi Islands, northeast of the Shumagins, south 

 shore of Alaska peninsula, No. 1159, W. H. Dall collector, 1 adult 

 female; explorations in Alaska of Lt. George M. Stoney, 1884, tag 

 Nos. 15, latitude 60° 10' N., longitude 160° 18' W., 1 adult female; 24, 

 latitude 60°22' N., longitude 168°45' W., 8 adult breeding females; 26, 

 latitude 61°3' N., longitude 167°55' W., 20 fathoms, June 7, 1884, 335 

 females, 16 males; 27, latitude 62°15' N., longitude 167°48' W., 20i/ 2 

 fathoms, June 13, 1884, 78 females, 14 males; 28, latitude 62°54' N., 

 longitude 166°38' W., 22 fathoms, June 14, 1884, 4 females, 1 male. 

 British Columbia : Berry Point, north arm, Vancouver, 15 to 30 

 fathoms, June 14, 1928, 1 adult breeding female. 



Distribution. — Kamchatka (Dershavin) ; Korea Straits (Ii). The 

 above records show that this species is distributed all along the Pacific 

 coasts of Asia and North America from the Korean Straits to Van- 

 couver in water up to 22 fathoms in depth. 



Remarks. — This species may be recognized by the following char- 

 acters : 



(1) There are no grooves or ridges on the thoracic and abdominal 

 somites. 



(2) The carapace is produced into a short triangular pointed rostral 

 plate. 



(3) The antennal scale (fig. 89, a) is seven times as long as broad. 



(4) The endopod of the third to the eighth thoracic limbs has the 

 sixth joint subdivided into five to eight subjoints. 



(5) The telson (fig. 89, b) is broadly spatulate in shape, 2,y 2 times 

 as long as broad at the base, apex broadly rounded and armed with 

 two pairs of spines, the inner only half as long as the outer ; the lateral 

 margins are armed with a continuous series of spines, rather short and 

 extending throughout the whole margin; distally the spines tend to 

 be arranged in series of two or three smaller spines between each pair 

 of larger spines but the grouping is not nearly so obvious as it is in 

 A. costata or A. stelleri because of the very much shorter larger spines. 



