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Show 24 MR. R. GURXEY OX THE [May 12, •2. The Metamorphoses of the Decapod Crustaceans Mgeon (Crangon) fasciatus Risso and Mgeon {Crangon) trispinosus (Hailstone). By R O B E R T G U R N E T , B.A., F.Z.S. [Received March 2, 1903.] (Plates Y. & VI.*) During a residence of nearly a year at Plymouth, I was able to obtain and study a very great variety of Decapod larvae, and among them those of five species of Crangonidae. Of these five species, which it will be convenient here to consider as all belonging to the genus Crangon, three, namely Crangon vulgaris, C. spinosus, and C. nanus, have already been fully described by Bars, and C. vulgaris has also attracted the attention of a number of other workers in this field of research. The remaining two species, Crangon trisjmiosus and C. fasciatus, have remained hitherto unrecognised. The identity of these larva? was placed beyond all doubt both by hatching them from the egg and by observing the last moult to the adult form. Attempts at rearing the larva? hatched in the Laboratory were quite unsuccessful, though with the same methods (plunger jars) and under apparently similar conditions I was able to rear the larva? of Pandalina brevirostris right through to the postlarval form. Bescription of the Larvce. I. CRAXGOX FASCIATUS (Risso). Length of larva on hatching, exclusive of the rostrum f, T8 to 2-05 mm. Average of 24 specimens 2*0 mm. The rostrum measures about T7 mm. at this stage. The general form of the body is slender, the abdominal segments being not distinctly narrower than the thorax. The carapace is prolonged anteriorly into a slender, pointed rostrum, reaching about half the length of the peduncle of the first antenna. Below, its margin is evenly arched and without teeth, ending in front, at the base of the second antenna, in a blunt process. There is no fold of the carapace over the eyes, so that the latter appear as prominent facetted areas of the carapace itself (see "Williamson, 1901, p. 113). In front of the eyes, and on either side of the rostrum, is a small knob-like process (see PI. V. fig. 1). I can find * For explanation of the Plates, see p. 30. f As here, so in the case of C. trispinosus the rostrum is left out of account, as measurements from the anterior edge of the eye to the edge of the lateral lobe of the tail-plate give a truer basis of comparison for body-length of different species. |
