164 



the possibility of separating specimens that deviate maximally from the 

 type specimen into a special subspecies. 



In the structure of pereopods, length of antennae, and several other 

 features, many species — S. curvidactyla and S. curilensis and, to a lesser 

 extent, S. incerta and S. langhansi — come closer to S. crassicornis, and 

 form a single group. Some general features of the species of this group 

 are also found in S. borealis and S. vosseleri but since several significant 

 differences exist, they cannot be included in the crassicornis group. 



Distribution: A circumoceanic warm-water species that enters, how- 

 ever, the cold-water regions of the Atlantic Ocean (up to 64° N) and 

 Antarctica (66° S). In the Pacific Ocean it is not found north of 44° N. 

 It is absent in the northeastern part of the Arabian Sea where there is 

 a distinct subsurface layer deficient in oxygen. It inhabits mostly the 

 upper 500 m but is also known from catches of 1 ,400-2,700 m. Repeat- 

 edly found in surface waters. According to the data of Thurston (1976b) 

 its diurnal migrations are of large amplitude. It can produce phosphores- 

 cence in the form of running violet flashes moving from the proximal to 

 the distal end of the pereopods. 



2. Scina curvidactyla Chevreux, 1914 (Fig. 60) 



Chevreux, 1914: 3, 1919: 12; Wagler, 1926: 328, 1927: 92; Barnard, 

 1932: 259; Shoemaker, 1945a: 230; Vinogradov, 1960a: 228. . 



Sexually mature specimens vary in length from 13 to 23 mm 

 (females). 

 140 The body has well-developed dorsal and lateral keels originating 



at the base of antennae I. Antennae I exceed the length of the pereon, 

 reaching 2/3 the body length. 



The mouth cone is somewhat less distinct than in 5. crassicornis. 

 The outer lobe of the maxillipeds is oval, not tapering sharply to the 

 distal end; the inner lobe reaches almost half the length of the outer and 

 on its rounded distal end bears two small apical setae. 



Pereopods III and ~IV are identical in length and structure, their rod- 

 shaped 4th and 5th segments roughly equal, the thin 6th segment slightly 

 shorter than either of them; the claw is short and curved. The 2nd segment 

 of pereopods V is denticulate on the anterior and posterior margins but 

 the denticles more distinct on the posterior margin; the slightly curved, 

 long distal process bears 1-3 denticles on the anterior margin; the 4th 

 segment is slightly longer than the 5th; the 6th segment is very thin and 

 short, about 1/4 the length of the 5th; the claw is very small. Pereopods 

 VI, unlike in S. crassicornis, are only slightly shorter than pereopods V; 

 the 2nd segment is slighdy denticulate in the middle part of the posterior 

 margin; the 4th segment is markedly longer than the 5th; the 6th segment 

 is longer and stronger than in pereopods V; the claw is very small and 

 curved. Pereopods VII are weak; the 6th segment is roughly equal to the 



