96 BULLETIN OF THE 



SEKGESTID-aEJ. 



Sergestes arcticus Kkuyer. 



OveisigtVidensk. Sclsk. Forhandl. Kjiibt'iihaven, 1855, p. (G) ; Monograph. Sergostes, 

 Vidensk. Selsk. Skv., V., Naturvidensk. inathem. Afh., IV. pp. 210, 276, 

 PL IIL figs. 7a -7^, PL V. fig. 16, 1856. 



Smith, Proc. National Mus., Wasliiiigton, III. p. 445, 18S1. 



Plate XVI. Fig. 4. 



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

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

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

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

 pleurobranchia on the antepenultimate somite, and on the pienultiniate somite 

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

 last somite is without branchia; ; or, indicating the simple pleurolamella) by 

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



XII. Xtll. XIV. Total. 



(2) 



1 







Pleurobranchia, C 1' 1' 1' 2 2 7 



8+(2) 



* Boas (Studier over Decapodernes Stsegtskabsforhold, A^'idensk. Selsk. Skr., VI., 

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

 dimentary arihrobranchia 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 " mastibranehia" (epipod) and one 

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

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

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

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

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

 the next three somites, and one I'lumeand a rudimentary mastibrancliial j>late to the 

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

 apparently indicate an arrangement of the branchicc nuuh like that wlii'eh I have 

 given above, or even nearer to that of S. robustus described bej'ond, but it is very 

 unlike the arrangement indicated by his formula for the genus. 



