940 DE. H. J. HANSEN ON OBUSTACEANS [DeC. 1, 



species. In the full treatment (" The Stalk-eyed Crustacea. — Eep. 

 on an Explor. off the West Coast of Mexico . . .," Mem. of the 

 Mus. of Compar. Zool. vol. xviii. 1895) he communicates extensive 

 descriptions and a series of figures of the same 3 species, but he 

 withdraAVs 2 of them as synonyms to earlier known forms ; one of 

 these, jS. Jialia, must, however, be re-established. 



'L'he result is that of Scrr/estes and Serr/ia, taken together, 

 59 species have been established, of Sciacaris 1 — in all CO species, 

 of which 7 have been withdrawn by various authors, but only 5 

 with good reason ; so that we have the preliminary result : 55 

 species. 



The development of Sergestes was first and most fully eluci- 

 daled by C. Claus. In 18G3 (" Ueber eiuige Schizop. und niedere 

 Malacostraken Messina's," Zeitschr. f. wiss. Zool. B. xiii. 1863) 

 Claus describes a larva which he names AcaniJiosoma, without, 

 however, being able to indicate its relations ; but he (pp. 437- 

 439) correctly refers Mastigopus, Leuckart (1853), to a larva of 

 Sergestes. In 1876 (Untersuch. zur Erforschung der Geneal. 

 Grundlage des Crustaceen-Systems) he shows all the principal 

 features of the metamorphosis : he has found a Protozoea-&ia.ge, 

 and states the zoea described by Dohrn as Elaphocaris, Acan- 

 tJiosoma, and Mastigojms to be successive stages of the deve- 

 lopment. One point is of special interest, viz. his statement that 

 the two posterior pairs of trunk-legs, which are well developed 

 with long exopods in the Acanthosmna, are thrown off by the 

 moulting to the Mastigopus-stnge, and then grow out again ; they 

 become " sichtbar als kurze Schlauche, die wir an griisseren und 

 iilteren Larven in verschiedenen Uebergangsstufen zu kleinen 

 Piissen sich entwickeln sehen" (Zeitschr. w. Zool. p. 438). — Some 

 months before the " Untersuchungen " of Claus appeared v. 

 Willemoes-Siihm published (" Prelim. Eemarks on the Development 

 of some Pelagic Crust.," Proc. Eoy. Soe. Lond. vol.xxiv. 1876, and 

 Ann. & Mag. Nat. Hist. ser. 4, vol. xvii.) a short paper, in which 

 he states that Elaphocaris, Dohrn, is the zoea of Sergestes, and that 

 the development passes through an AmijJiion-stage &c. ; but on the 

 Mastigo2nis-&tage and its want of the two posterior pair of trunk- 

 legs he says nothing. — In Bate's ' Challenger ' Eeport 30 pages 

 and several plates are occupied by the representation of a series of 

 Elaphocaris, Acanthosoma, Mastigojms, and considerations about the 

 development. On p. 383 he says : " By tracing the several stages, 

 we may safely conclude, from the direct structural affinities, that 

 Mastigopus is a young Sergestes." This is correct, but when he 

 really tries to establish any limit between Mastigopus and Sergestes 

 he is not fortunate, nay, in the description of Serg. longispinus. 

 Bate (pp. 417-18), he even writes : " The fourth and fifth pairs are 

 entirely absent," and later on he is " inclined to think that their 

 absence is owing to the early stage of development " ; thus his 

 Sc.rg. longispinus is a young Mastigopus with the legs referred to 

 still less developed than in the form he in the earlier part (pp. 376- 

 77) describes as Mastig. acetiformis, Bate. Thus the differences 



