1896.] © OF THE GENUS SERGESTES, 967 
Ale., not included) of Group II. The 4 other larval species, all 
described by Bate, are established on very young specimens, 
between 3°5 and 7 mm. long, and are probably all or almost all 
but young stages of some of the species described above, but I 
have not been able to refer them with certainty. 
vil. Remarks on SciacaRis and Prtantpium of Bate. 
To the genus Sciacaris, Bate, only one species, S. telsonis, Bate 
(p. 438, pl. xxviii. fig. 1), has been referred, and this is a Mastigo- 
pus-stage, which agrees so closely with Sergestes that I must 
consider it as being the larva to a Sergestes-species, and in the 
tabular view given above I have referred it to Group I. 
The genus Petalidium, Bate, was established on one species, 
P. foliaceum, Bate (p. 349, pl. lx.), which is very deficiently known 
as the specimens were extremely mutilated, without legs and with 
the uropods broken off. But the branchie are very interesting. 
Bate ascribes its arthrobranchie to mxp.° and trl.'-trl.*, bat 
according to his analytical figure I believe them rather to be 
pleurobranchiz as in Sergestes; besides, he mentions and figures 
large foliaceous plates to trl.’, trl.*, and trl.*, answering to the 
lamellz in Sergestes. I should not have mentioned this interesting 
but very imperfectly known form if I had not met with rather 
similar pleurobranchial lamelle in S. sanguineus, Chun (Sitz. 
d. k. Preuss. Akad. d. Wiss. zu Berlin, 1889, p. 538, Taf. iii. 
fig. 1). 
cincasidias to a careful comparison between the largest type 
specimen of S. sanguineus, Chun, 9°5 mm. long, and Kréyer’s 
representation of his S. obesus, Kr. (p. 257, tab. iv. figs. 10, a), 
and the fragments of his single type specimen, the two species are 
identical, and the name given by Kroyer must be adopted. The 
largest specimen seen by me is a Mastigopus, perhaps not more 
than half-grown. For the recognition of the species it may at 
once be mentioned that several very characteristic particulars have 
been figured; thus Kroyer figures the eye, the antennular peduncle, 
and the uropods, and mxp.° and the trunk-legs are represented by 
Chun. Next I shall give a short description of the largest 
specimen. The rostrum is rather short, considerably shorter 
than the diameter of an eye, almost horizontal, slender, with a 
dorsal spine at the basis. No supra-ocular spines, but the hepatic 
spine and the gastro-hepatic groove are well developed. The eye- 
stalks rather short, but the eyes nevertheless reaching beyond the 
second joint of the antenn. ped., the eye-stalk with the eye, seen 
from the side, inverted conical, and the distal part of the cornea 
forming almost a hemisphere at the end of the cone—a shape 
very different from that in the Mastigopus of Sergestes. The 
antenn. ped. is short, the first joint much longer than the other 
two taken together, thus longer than in any above-described 
Mastigopus of the same length. Mxp.* very short, somewhat 
longer than trl.’ and very little longer than trl.?; trl.° is almost 3 
