96 BULLETIN OF THE 



SERGESTID^. 



Sergestes arcticus Kroybr. 



Oversigt Vidensk. Selsk. Forhandl. Kjbbenhaven, 1S55, p. (6) ; Monograph. Sergestes, 

 Vidensk. Selsk. Skr., Y., Naturvidensk. matheru. Afh., IV. pp. 240, 276, 

 PL III. figs. 7a -7g, PI. V. fig. 16, 1856. 



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



Plate XVI. Fig. 4. 



In this species there is an epipod 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 Bomite 

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

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

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



8+(2) 



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

 Natuvidensk. mathem. At'h., I., 1880), for<S\ Frisii Krdyer, gives an epipod and aru- 

 dimentary arihrobranehia 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 

 pleurobranchia for the eighth somite, a single pleurobranchia for the ninth, a pleuro- 

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

 branchise for the thirteenth, and nothing for the last ; but under S. Kr&ytri he Bays, 

 "This Bpeciee has two well-developed pleurobranchia attached to the penultimate 

 Bomite of the pinion, two to the antepenultimate, one plume and a leaflike plate to' 

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

 first pair of gnathopoda " (second mazillipeds). This lasl statemenl of Bate would 

 apparently indicate an arrangement of the branchiae much liki- that which 1 have 

 given above, or even nearer to that of 8. robuatus described beyond, but it I 

 unlike the arrangement indicated by his formula for the genus. 



