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Show 1900.] FROM THE FALKLAND ISLANDS. 543 7. Apical lobes on based joint of first antennce.-This feature is found wanting by Sars in the species he calls splendens and gracilis, as also in his own species similis and mucronata. Of his antarctica he says: " Antennular peduncle slender, without any dorsal lobe, but with the outer corner of the basal joint produced into a sharp spine." Ortmann's species schotti agrees iu this respect with antarctica, except that the sharp spine instead of being small is very elongate. As already mentioned, it is not at all certain that the true splendens and gracilis of Dana are without the lobe, or that the true pellucida of Dana has it. The value of this character is further somewhat impaired by its variability, since in his description of bidentata Sars says: "In most of the specimens this lobe is divided into two acuminate lappets (fig. 3); but in some specimens, though differing in no other respect from the typical form, these lappets are much more numerous, forming a dense fringe along the free edge of the leaflet (fig. 4)." Dr. Ortmann says of gibboides, " basal joint of the inner antennae above with an oval, obliquely forward and outward pointed lobe;" and of pseudogibba, " basal joint of the inner antennae above with a triangular lobe, whose point is directed forward and outward." But the triangular lobe is not figured, and the oval one is, in the figure, itself apically pointed and verging on the triangular. There are also lobes occurring on the second and third joints of the first antennae which are available, though they have not yet been found important for specific discrimination. 8. The basal scale of the second antennce and the attendant basal spine.-The extent to which the scale reaches beyond the peduncle would be a useful character, but information on this point is rather deficient. Apparently bidentata is distinguished from all other species by the fact that its basal spine extends far beyond half the length of the scale. 9. 3Iandibular palp.-Unfortunately for several species the features of this palp are known imperfectly or not at all. Judging from Dana's figure of it in Euphausia superba, that species agrees in this particular with antarctica of Sars, in which the palp in question is very slender, its terminal joint being nearly as long as the median. This is not the case in pellucida Dana, mulleri Claus, bidentata Sars, splendens of Sars, or gracilis of Sars, the last having " the terminal joiut very small and oval in form." 10. Second maxilhe.-The shape, size, and armature of the apical joint seem to offer tangible characters for specific distinction, but such as can only be discovered by dissection. 11. Proportionate length of the joints in the three pairs of maxillipeds and the three developed pairs of perceopods.-The value that might attach to this character is strikingly illustrated by a comparison of the figures drawn by Sars of the last of these appendages in bidentata and antarctica. In the former species the third joint is shorter than the fourth, in the latter it is much longer than all the four succeeding joints combined. Unfortunately, beyond this one comparison, there is scarcely any definite and trustworthy 31)* |
