OCR Text |
Show 1896.] OF THE GENUS SERGESTES. 963 third segment is longer than the first or the second by one-half." Unfortunately Faxon does not describe or figure the sixth joint of mxp.3 I think that the species will prove to be different from S. incertus, m. When Faxon states that 6 large pleuro-branchiae and one smaller podobranchia are present on each side on tbe body, he certainly bas overlooked the 5 lamellae, which I have found in 8. incertus and the other species of the edwardsi-group. S. hamifer, Ale. & And., I will mention here, though I have not been able to insert it in m y tabular view. The description (1894) and the figure (1895) plainly show that it belongs to this group. As in mxp.3 " the propus is four-jointed," the species cannot be identical with S. edwardsl, Kr., but it is impossible for me to settle whether it be really valid or synonymous with one of the other species. Only two characters 1 have been able to detect, viz.: that mxp.3 seems to be still longer than in any other species, and that its fifth joint is curiously arcuated (see the figure); but it is difficult to say whether these two characters are valid, for instance, to decide whether the shape of the mentioned fifth joint may not be due to some artificial cause. The species must be reexamined. As mentioned above, I have examined five older Mastigopus-fortns, four of which have been elsewhere described. The older specimens, c. 10-15 mm. in length, are easily recognized from each other, and some few characters shall be pointed out; but the younger stages are more difficult, being more spiny, &c, and besides the materials seen by m e are rather insufficient, and the animals difficult to characterize without the aid of figures. The larvae are easily distinguished from all larvae in Group I. by the elongated and vigorous mxp.3, and from S. sargassl, Ortm., by tbe longer eye-stalks. In tbe old larvae the sixth joint of mxp.3 is divided into 4 subjoints (tbe oldest larval stage ot S. oculatus, Kr., is unknown to me, so that I cannot settle whether its two distal subjoints are divided as in S. edwardsl, Kr.), but tbe armature on the end and on the interior margin is very different from that in the adults. S. oculatus, Kr.-Kroyer has given a good representation (p. 243, tab. iii. figs. 5, a-f) ; Bate has also described and figured it (p. 406, pl. lxxiv. fig. 1). Both Kroyer and Bate figure, in m y opinion, the eye-stalks a little too long. The rostrum is short, seen from the side obliquely triangular, acute, and rather broad at the base ; the abdominal segments are dorsally smooth-even in a specimen but 6-5 m m . long-and on tbe ext. br. of urp. the exterior margin is ciliated in the total or almost the total length (in a larva 10 m m. long, c. T X T, measured with accuracy, of the length was naked). By the combination of these three characters the older specimens are easily recognized. The species is most decidedly the Mastigopus of' S. edwardsl, Kr.-S. brachgorrhos, Kr. (p. 272, tab. v. tigs. 13, a-b), is the young Mastigopus of S. edwardsl, Kr. I have examined Kroyer's type specimen, which is about 4 m m . long. |