96 BULLETIX OF THE 



SERGES TID-aS. 



Sergestes arcticus Kruyer. 



Oveioigt Vidensk. Selsk. Forliandl. Kjobenhaven, 1855, p. (G) ; Monograph. Sergestes, 

 Vidensk. Selsk. Skr., V., Naturvidensk. mathem. Afh., IV. pp. 240, 276, 

 PI. III. figs, la-lg, PI. V. fig. 16, 1856. 



Smith, Proc. National Mus., Washington, III. p. 445, 1881, 



Plate XVI. Fig. 4. 



In this species there is an epipocl and a well-developed podobranchia at the 

 base of the second maxilliped, and above its base a simple lamella in place of a 

 pleurobranchia, a large anterior pleurobranchia with a simple lamella back of it 

 on each of the three succeeding somites, a large anterior and a small posterior 

 pleurobranchia on the antepenultimate somite, and on the penultimate somite 

 two small branchiae, of which the posterior is very much the smaller, while the 

 last somite is without branchiaj ; or, indicating the simple pleurolamellae by 

 accents, the branchial formula* may be indicated as follows : — 



8+(2) 



* Boas (Studier over Decapodernes Steegtskabsforhold, Vidensk. Selsk. Skr., VI., 

 Natuvideiisk. mathem. Afh., I., 1880), for S. Frisii Kiciyer, gives an epipod and a ru- 

 dimentary arthrobranchia for the eighth somite and a single pleurobranchia for each 

 of the succeeding somites including the last. Bate (Ann. Mag. Nat. Hist., 5th ser., 

 VIII. p. 193, 1881), gives, for the genus Sergestes, a " mastibranchia" (epipod) and one 

 ])lcarobrancliia for the eighth somite, a single iilcurobranchia for the ninth, a pleuro- 

 branchia and pleurolamella each for the tenth, eleventh, and twelfth, two pleuro- 

 branchige for the thirteenth, and nothing for the last ; but under S. Kroycri he says, 

 "This species has two well-developed pleurobranchise attached to the penultimate 

 somite of the pereion, two to the antepenultimate, one plume and a leaflike plate to 

 the next three somites, and one plume and a rudimentary mastibranchial plate to the 

 first pair of gnathopoda " (.second maxillipeds). This last statement of Bate would 

 apparently indicate an arrangement of the branchiae much like that which I have 

 given above, or even nearer to that of S. robiistus described beyond, but it is very 

 unlike the arrangement indicated by his formula for the genus. 



