| OCR Text |
Show 1896.1 OF THE GENUS SERGESTES. 967 Ale, not included) of Group II. Tbe 4 other larval species, all described by Bate, are established on very young specimens, between 3*5 and 7 m m . 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. Remarks on SCIACARIS and PETALIDIUM of Bate. To the genus Sciacaris, Bate, only one species, S. telsonls, Bate (p. 438, pl. lxxviii. fig. 1), has been referred, and this is a Mastlgo-jpiis- stage, which agrees so closely with Sergestes that I must consider it as being tbe larva to a Sergestes-s-pecies, and in the tabular view given above I have referred it to Group I. The genus Petalldlum, Bate, was established on one species, P. follaceum, Bate (p. 349, pl. Ix.), which is very deficiently known as the specimens were extremely mutilated, without legs and with the uropods broken off. But the branchiae are very interesting. Bate ascribes its arthrobranchiae to mxp.3 and trl^-trl.3, but according to his analytical figure I believe them rather to be pleurobranchiae as in Sergestes; besides, he mentions and figures large foliaceous plates to trl.1, trl.2, and trl.3, answering to the lamellae in Sergestes. I should not have mentioned this interesting but very imperfectly known form if I had not met with rather similar pleurobranchial lamellae in S. sanguineus, 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 S. sanguineus, Chun, 9*5 m m . long, and Kroyer's representation of his S. obesus, Kr. (p. 257, tab. iv. figs. 10, a-f), aud 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 m e 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, tbe antennular peduncle, and the uropods, and mxp.3 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.3 very short, somewhat longer than trl.1 and very little longer than trl.8; trl.3 Is almost 3 |
