940 DR. H. J. HANSEN ON CRUSTACEANS [Dec. 1, 
species. In the full treatment (“ The Stalk-eyed Crustacea.—Rep. 
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 
withdraws 2 of them as synonyms to earlier known forms ; one of 
these, S. halia, must, however, be re-established. 
The result is that of Sergestes and Sergia, taken together, 
59 species have been established, of Sceacaris 1—in all 60 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of which 7 have been withdrawn by various authors, but only 5 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- 
dated by ©. Claus. In 1863 (“ Ueber einige Schizop. und niedere 
Malacostraken Messina’s,” Zeitschr. f. wiss. Zool. B. xiii. 1863) 
Claus describes a larva which he names Acanthosoma, without, 
however, being able to indicate its relations; but he (pp. 487— 
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 Protozoéa-stage, 
and states the zoéa described by Dohrn as Hlaphocaris, Acan- 
thosoma, and Mastigopus 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 Acanthosoma, are thrown off by the 
moulting to the Mastigopus-stage, and then grow out again; they 
become “ sichtbar als kurze Schlauche, die wir an groésseren und 
iilteren Larven in verschiedenen Uebergangsstufen zu kleinen 
Fiissen sich entwickeln sehen” (Zeitschr. w. Zool. p. 488).—Some 
months before the “ Untersuchungen ” of Claus appeared v. 
Willemoés-Suhm published (“ Prelim. Remarks on the Development 
of some Pelagic Crust.,” Proc. Roy. Soc. Lond. vol. xxiv. 1876, and 
Ann. & Mag. Nat. Hist. ser. 4, vol. xvii.) a short paper, in which 
he states that Hlaphocaris, Dohrn, is the zoéa of Sergestes, and that 
the development passes through an Amphion-stage &c.; but on the 
Mastigopus-stage and its want of the two posterior pair of trunk- 
legs he says nothing.—In Bate’s ‘Challenger’ Report 30 pages 
and several plates are occupied by the representation of a series of 
Elaphocaris, Acanthosoma, Mastigopus, 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 
Serg. 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 ditlerences 
