418 REPOET OF COMMISSIONER OF FISH AND FISHERIES. [74] 



but with a shallow median sulcus on the third and fourth somites. 

 [There are apparently similar sulci on the abdomen of S. arcticus.] The 

 pleura of the first three somites are large and i)roject backward in an 

 angle, while the pleura of the fourth and fifth somites project backward 

 quite as far, but have the outline more rounded. The sixth somite is 

 about as long as the antennal scale, considerably more than half as high 

 as long, and strongly compressed. 



The telson is considerably shorter than the sixth somite, flattened and 

 slightly sulcated above, with a deep lateral groove each side, acutely 

 angular at the tip, and ciliated along the edges. The inner lamella of 

 the uroi)od is about as long as the telson, about three times as long as 

 broad, and lanceolate at the top. The outer lamella is between a third 

 and a fourth longer than the inner, about a fourth as broad as long, the 

 outer margin terminates in a strong tooth about two-thirds of the way 

 from the base to the tip, and the tip is narrow, but rounded. 



The peculiar sexual appendages (Fig. 6) of the first somite of the 

 pleon have essentially the same structure as in iS. arcticus, but are much 

 more complicated than would be inferred from the figures of that sjje- 

 cies given by Kroyer. The appendages of the two sides are usually 

 hooked together along the middle line (/i), but are really entirely dis- 

 tinct. Each is attached by a narrow process {a) to the protopod of the 

 pleopod, and is divided by more or less distinct sutures into three por- 

 tions. The outer portion, that next the protopod, projects above the 

 point of attachment in a narrow process, and below the point of at- 

 tachment in a broad lamellar lateral expansion, and below this in a 

 long, flat, chitinous stylet (6) terminating in a sharp hook below a 

 rounded sinus in the extremity. The middle portion projects below 

 and alongside of, but far beyond, the hooked stylet (&), in a compli- 

 cated appendage divided distally into three membranaceous and hook- 

 bearing processes (e,/, g) and bearing two slender and unarmed stylets 

 (c, d) ; and each of the membranaceous processes is armed along one 

 edge with a series of peculiar chitinous hooks retracted within invag- 

 inated i^apillaB (Fig. 6^), and at the tip with a larger and somewhat dif- 

 ferently shaped but similarly retracted hook (Fig. Q'^). The lateral 

 hooks themselves are semi-mushroom shaped, like those which serve to 

 hook together the inner rami of the pleopods in many crustaceans, and 

 very much like those along the mesial edge (/i) of this same appendage 

 but larger. The terminal hooks are more properly hook-shaped, as 

 shown in the figure, but are broad at the tips. The invagination of the 

 membrane around the hooks is possibly due to contraction in the alco- 

 holic specimens, but the hooks are similarly retracted in all the speci- 

 mens of S. arcticus which I have examined, their bases appear to be con- 

 nected with strong muscular fibers, and I think there is little doubt that 

 the hooks are capable of being retracted in life. The mesial portion of 

 the appendage is thin, lamellar, longitudinally folded, and armed along 

 the mesial edge with great numbers of senii-mushroom-shaped hooks, 

 which serve to attach together the appendages of the two sides. 



