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Show 542 MR. E. J. MIERS ON [June 6, prominences on which the genital apertures are placed are quite short and unarmed. Reference should have been made in my previous paper ou Mauritian Crustacea obtained by the British Museum from M. Robillard, to two species which were received from him last year. One of these is a fine and large specimen of an Alpheus, which I refer somewhat doubtfully to the Alpheus rapax of Fabricius, as described by De Haan. It has the rostrum prolonged backward as a median dorsal carina to the middle of the carapace, and in other particulars agrees excellently well with De Haan's description1, but differs from the figure in having the mobile finger of the larger chelipede vertically deeper than in that author's figure and subtruncated at its distal extremity. The other species is an apparently undescribed species of Pseudibacus, Guerin-Meneville, a genus previously unrepresented in the collection of the British Museum. PSEUDIBACUS PFEFFERI, sp. n. (Plate XXXVI. figs. 2, 3.) The carapace is broader than long; the ambulatory legs are concealed beneath its lateral prolongations. The upper surface of the carapace is nearly smooth ; the antero-lateral margins are thin, acute, and regularly crenulated on each side; a notch marks apparently the line of demarcation between the cervical and postcervical regions ; in front of the lateral notches are seven or eight,and behind them eleven or twelve crenulations ; a longitudinal depression exists on each branchial region, not far from the lateral margins. The median dorsal line of the carapace is marked by a longitudinal ridge or keel, which originates at a short distance behind the anterior margin, and on the cardiac region is bifurcated-the two carinse thus formed enclosing a median depression or shallow pit, behind which they reunite and are continued as a simple ridge to the posterior margin of the carapace ; the anterior and the two median carinae are each divided into three or four obscurely indicated lobes ; the posterior carina is entire, but terminates in a small tubercle on the posterior margin of the carapace. The anterior margin of the front is bisinuated in its median portion, where the basal lobe of the rostrum is articulated with it; the terminal plate of the rostrum is transverse, with the extremity subacute, and is divided through about half its length by a median, longitudinal, nearly closed fissure. The orbits are situated about midway between the median line and the lateral angles of the carapace, and are merely closed by a process of the basal antennal joint as in Pseudibacus gerstaeckeri. The postabdomen resembles that of P. gerstaeckeri as described by Dr. Pfeffer in all essential characters : thus the second to fifth segments are each armed with a median dorsal carina, which slopes obliquely downward to the anterior margin (except on the second segment), and is posteriorly produced and ends in an acute tooth on the fourth and fifth segments; the sixth segment has a small median tubercle on its posterior margin, and the seventh three at the line of demarcation between the 1 Vide Crustacea, in Siebold's 'Fauna Japonica,' p. 177, pl. Ixv. fig. 2 (1849). |
