1896.] OF THE GENUS sbugbst^s. 955 



broad — thus conspicuously more narrow than in S. mediterraneus, 

 m. ; and the outer margin beyond the spine but slightly concave. 

 The branchiae (comp. the notes of S. I. Smith in Bull. Mus. Comp. 

 Zool. vol. X. p. 9C) do not seem to present any character fit for 

 use. S. arcticus, Kr., is smaller than the other species when the 

 eyes obtain the black colour. 



Above I have mentioned that S. ruhroguttatvs, Wood-Mas., from 

 the Indian Ocean is, in my opinion, a valid species, as the exter. 

 br. of urp. is described and figured (Ann. & Mag. Nat. Hist. ser. 6, 

 vol. viii. p. 354) to be much more narrow than in 8. arcticus, Kr., 

 and without the spine on the outer margin. 8. Icroyevi, Bate, and 

 S. preliensilis. Bate, are unknoM'n to me ; they have the same 

 branchial foriDula as 8. arcticus, but a new investigation of both 

 species is much needed ; perhaps 8. ruhroguttatus. Wood- Mas., is 

 synonymous with 8. hroyeri. Bate. 



Of 8. arcticus, Kr., our museum possesses a series of all stages from 

 the AaintJwsoma (inch) to the mature form. One of these stages 

 is 8. rinJcii, Kr. Kroyer's representation (p. 2G5, tab. ii. fig. 3, 

 a-f/) corresponds well with specimens of 8 mm. in length, rostrum 

 not included, and is rather good ; thus he describes and figures the 

 eyes with their long stalks, the very characteristic antenn. ped., 

 the shape of the squama, the dorsal spines on the abdomen, the 

 long pleopods, the uropods with their exterior branch being very 

 characteristic for the young Mastigojnis, viz. 6'5 times longer than 

 broad and the ciliated part of the exterior margin considerably 

 longer than in the adult, finally the telson, which has a shape very 

 diiierent from that found in the adult — but the representation of 

 the carapace is deficient (see later on) and misleading in one par- 

 ticular. Thus he describes the rostrum as being short, but it must 

 already then have been broken ofi in one or two of his specimens ; 

 in reality it is about as long as the eye-stalks (without the eyes), and 

 adorned at the basis with a dorsal spine almost as long as the 

 diameter of the eye. 



The largest specimen oi Acanthosoma, which, however, I shall not 

 try to describe, is, the rostrum not included, 5-3 mm. in length, 

 and with the rostrum (which reaches somewhat in advance of 

 the eyes) c. 6-6 mm. long. Among the type specimens of Kriiyer 

 I find tvs'o specimens, which must be the stage immediately suc- 

 ceeding the Acanthosoma ; one specimen is with the rostrum 6'9 

 mm. long, but from another locality I have seen a specimen in the 

 same stage measuring even 8 mm. This stage differs considerably 

 from that described by Kroyer, and therefore a short account of it 

 shall be given. The rostrum is exceedingly long, reaching a little 

 in advance of the eyes, on the distal part adorned with some short 

 and fine setse, and at the basis originates a setaceous dorsal sj)ine, 

 which is adorned with some short and fine setse and is longer than 

 the diameter of an eye. The supraocular spine is well developed, 

 and the hepatic spine exceedingly long, considerably longer than 

 the diameter of an eye ; just in front of the gastro-hepatic groove 

 is observed a short protuberance in the median line. The eyes 



