946 Bn. n. j. Hansen on ckustaohans [Dec. 1, 



iv. Synonymical and other Bemarhs. 



Before proceeding to a systematic arrangement, founded upon 

 the characters mentioned, it will perliaps be convenient to under- 

 take some reduction of the species, especially of the adult forms, 

 with a view to freeing the next chapter, containing notes on tho 

 structure of the species and their larvte, from these disturbing 

 investigations. 



The single species established by de Natale, S. arachnipodus 

 (p. 19, Tav. ii. fig. 1), is quite anrecognizable to me, and will, in 

 my opinion, never be interpreted with certainty ; therefore I have 

 omitted it from the systematic arrangement. 



Of the 15 species described by Kroyer, only 4 {S. frisii, Kr., 

 -§. arcticiis, Kr., S. cornuius, Kr., S. edivardsi, Kr.) have been 

 established upon adult animals. Bate, Chun, and Ortmanu have 

 already considered S. frisii, Kr., to be identical with S. atlaniicus, 

 M.-Edw., but when Bate (oji. cit} p. 389) furthermore withdraws 

 S. areiieiis, Kr., this is, as pointed out by Ortmann, quite wrong. 

 Of the remaining 11 species 8 are true Sergestes-\s>x\'iB, while the 

 3 others, viz. S. obesus, Kr., S. caiidatus, Kr., and S. serrulatus, Kr., 

 must be removed from the genus. S. ohesus, Kr. (p. 257, tab. iv. 

 fig. 10, a-f) is a very curious form ; the single Kroyerian specimen 

 had been dissected and most of (he pieces are preserved, but an 

 investigation of the type specimens of S. sarwjtdneus, Chun (1889), 

 proved that this form is identical and that both species have been 

 established upon larvaj which differ so much from the Mastigopus 

 of Sergestes that the species must be removed from this genus, and 

 it will be discussed later on under Petalidium, Bate. S. caiidatus, Kr. 

 (p. 270, tab. V. fig. 14, a-d), is a very young Penceus that has just 

 passed the Ilysis-atage (Krdyer's representation of the trunk-legs 

 is not correct, as his type specimen possesses a well-developed chela 

 on trl.', behind which pair are found the basal joints of 4 pairs). 

 S. serndnlus, Kr. (p. 208, tab. iv. fig. 12, a-g) is a very young 

 Acetes, M.-Edw. Finally, S. lacinlatus, Kr. (p. 274, tab. v. 

 fig. 15, a-e), is, as already pointed out by Ortmann, identical with 

 S. eornieidum, Kr. 



Of the species described by Stimpson only one is adult, viz. 

 S. jtaeiflcus, Stimps. (p. 45), and it is, in my opinion, identical with 

 S. atlaniicus, M.-Edw., as the differences which the author states 

 to exist between his species and Kroyer 's description of S. frisii, Kr., 

 are of no value. The fact is that the hepatic spine is placed a 

 little more behind than in Kroyer's figure, in which also the 

 trunk-legs are delineated a little shorter than they are in the 

 animals. Of the other species, S. loiujicaudatus, Stimps., and 

 Sergia remipes, Stimps. (p. 4G), can, in my opinion, scarcely be 

 recognized without examination of the type specimens. 



Of Serg. meyeri, Metzger (p. 302, tab. vi. fig. 7), I have 



' I always quote tlie ' Ohalloiigoi- ' Report, not liis preliminary paper ; as to 

 Kroyer, I refer l-o hia monograph, omitting his earlier descriptions without 

 figuroa. 



