_1896.] OF THE GENUS SERGESTES. 951 
To this group further belong *S.hamifer, Alc. & And., which 
I am not able to recognize, and the following larve: S. znter- 
mecdius, Bate, S. diapontius, Bate, S. fermerinku, Bate, S. spini- 
ventralis, Bate, and S. ventridentatus, Bate, several of which 
certainly belong to some of the species in the tabular view, but I 
cannot recognize them; S. macrophthalmus, Stimps., in all proba- 
bility being a younger S. vigilaw, Stimps.; finally S. brachyorrhos, 
Kr., which is a very young larva of S. edwardsii, Kr. (see later on). . 
S. arachnipodus, de Nat., and S. profundus, Bate, I have not 
been able to refer to any one of the groups; to Petalidium is 
' transferred S. obesus, Kr. (S. sanguineus, Chun), and excluded as 
not belonging to the genus are S. serrulatus, Kr., and S. caudatus, 
Ken; 
vi. Notes on the Species of Growp I. 
A.a. S. tenviremis, Kr. The specimen described by Kroyer 
(p. 255, tab. iv. fig. 11, a—b) is a hardly half-grown Mastigopus ; 
S. longicollus, Bate (p. 421, pl. Ixxvii. fig. 1), is almost (or perhaps 
fully) adult; S. junceus, Bate (p. 416, pl. Ixxvi. fig. 1), is the 
young Mastigopus, 6 mm. long, with dorsal spines on the 4th— 
6th abdominal segments. I have examined a specimen 23 mm. in 
length, which had just obtained the black eyes; the species grows 
at least somewhat longer before maturity, but the mature form is 
unknown. The obtaining of black eyes does not always take place 
at the same length of the animal, as a specimen with the larger, 
oblique, yellowish eyes is even 26 mm. long. The species is easily 
separated from all other known forms by the combination of two 
characters: the very long and slender body with the long distance 
between the eye-stalks and the mouth-organs, and the ciliated 
parts on the ext. br. of urp. occupying, in the older forms scarcely 
3, in the younger alittle more than + of the exterior margin. The 
quoted figure of S. longicollus, Bate (pl. lxxvii.), gives a tolerably 
correct notion of the species. 
It may further be added that of the two branchiz above trl.’ the 
first is long and the second a little more than half the length of 
the first and but a little shorter than the first branchia to trl.*, 
while the second above trl.* is somewhat smaller, but still very well 
developed. J have seen specimens of this species from numerous 
localities in the Atlantic, northward to lat. 32° 16’ N., in the 
Indian Ocean, and in the Pacific as far as the Matelota Islands 
and lat. 16° 8’ 8., long. 111° 50’ E. 
A.b.a. S. atlanticus, M.-Edw. As to the synonymy etc., see 
above. The best representation of this very common species is 
given by Kroyer (S. frisw, Kr., p. 235, tab. i. fig. 1,a—-v). The 
sixth joint of mxp.’ consists of 6 subjoints, the 4 distal of equal 
length and each of the 2 proximal as long as 2 of the distal 
subjoints together. The branchial formula as in S. japonicus, Bate 
(S. mollis, Smith), viz. a podobranchia and a lamella to mxp.’, 
a pleurobranchia and a lamella to mxp.’ and trl.'-trl.’, finally 2 
pleurobranchiz to trl.*, but the branchiz are longer than in S. mollis, 
Smith (Rep. Comm. Fish and Fisheries f. 1885, pl. xx. fig. 5), and 
