189G.] OF TUB GENUS SBnGESTES. / 967 



Ale, not included) of Group II. The 4 other larval species, all 

 descrihed 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. 



viii. Bemarks on Sciacabis and Petalidium of Bate. 



To the genus Sciacaris, Bate, only one species, S. telsonis, Bate 

 (p. 438, pi. Ixxviii. fig. 1), has been referred, and this is a Mastujo- 

 j(tw-stage, which agi'ees so closely with Sergestes that I must 

 consider it as being the larva to a lSei-f/cstes-ii\)ecies, and in the 

 tabular view given above I have referrefl it to Group I. 



The genus Petalidium, Bate, was established on one species, 

 P. foliaeeum, Bate (p. 349, pi. Ix.), which is very deficiently known 

 as the specimens were extremely mutilated, without legs and with 

 the iiropods broken off. But the branchiae are very interesting. 

 Bate ascribes its artbrobranchise to mxp.' and trL'-trl.', but 

 according to his analytical figure I believe them rather to be 

 ])leurobraiichia) as in Sergestes ; besides, he mentions and figures 

 large foliaceous plates to trl.', trl.°, and trl.% answering to the 

 lamellae in Sergestes. I should not have mentioned this interesting 

 but very imperfectly known form if 1 had not met with rather 

 similar pleurobranchial lamellae in S. sanquineus, Chun (Sitz. 

 d. k. Preuss. Akad. d. Wiss. zu Berlin, 1889, p. 538, Taf. iii. 

 fig. 1). 



According to a careful comparison between the largest type 

 specimen of 8. sanguineus, Chun. 9-5 mm. long, and Kroyer's 

 representation of his ;S^. ohesus, Kr. (p. 257, tab. iv. figs. 10, Or-f), 

 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 thau trl.' and very little longer than trl.°; trV is almost 3 



