OCR Text |
Show 28 MR. E. J. MIERS ON CRUSTACEA FROM [Jan. 14, and emarginate rostrum. It is extremely difficult to find reliable characters by which to define the genera, as the species pass into one another by almost insensible gradations. At one end of the series are those which belong undoubtedly to the genus Libinia, in which the carapace is triangulate rather than orbiculate, with a distinct supraocular tooth, the rostrum prominent, with the spines coalescent and divergent only toward the apex, which thus appears notched, the orbits circular and well defined, with usually a single closed fissure above, the basal joint of the antenna? moderately dilated, and the leg3 usually of moderate length, the first pair rather slender in the male. At the opposite extremity of the series are the species of Doclea in which the carapace is orbiculate in outline, the rostrum very short, the supraocular spine absent, the basal joint of the antennae narrower, the orbits scarcely defined at all below, the legs usually very long, those of the first pair in the male short, with the palm dilated. The genus Libidoclea ol Milne-Edwards and Lucas is somewhat intermediate between the two former, having the triangulate carapace, prominent rostrum, dilated basal antennal joint of Libinia, with the incomplete orbits and long legs of Doclea; the typical species, L. granaria (Edw. & Luc. in D'Orbigny's Voy. Amer. Merid. vi. Crust. p. 8, pi. iii. fig. 1 & pi. iv. fig. 1, 1845), from Valparaiso, possesses an additional character in the existence of a notch on the anterior margin of the third joint of the outer maxillipeds; and the tooth in the middle of the outer margin of the basal joint of the antennae is very strong; the former of these fails, however, in the Libidoclea coccinea of Dana (U.S. Expl. Exp. xiii. Crust, p. 88, pi. i. fig. 3), from Patagonia, which also has a shorter rostrum. In certain species of Libinia (L. emarginata) there is a small blunt tooth on the outer margin of the basal antennal joint. There appears, then, to be no alternative between restricting the genus Libidoclea, by adopting the single character of the emarginate third joint of the outer maxillipeds, or extending its definition until it shall include all the species intermediate between the two older genera. The former is perhaps the preferable course, as, if the latter were adopted, it would be impossible to assign any definite characters to the genus. DOCLEA ORIENTALIS, sp. n. (Plate II. fig. 1.) The carapace is convex and subpyriform, with six tubercles in the middle line, of which the first three are on the gastric, two (one more elevated) on the cardiac, and one on the intestinal region; none of these are large and spiniform. There are two prominent tubercles on the lateral anterior margins, one of them placed at some distance behind the orbits, and one on the sides of the branchial region. There are four small tubercles on the front of the gastric region, forming, with the first of the median series, a figure *. * , seven or eight on the branchial region, on each side, and three on the pterygostomian region. The rostrum is short, but little longer than broad, and notched to its middle. The orbits have a supraocular tooth, a wide hiatus above, and two fissures below. The basal joint of the antennae is rather |