OCR Text |
Show 1901.] CRUSTACEAN FROM THE SOUDAN. 99 The carapace is somewhat less enlarged and, according to A. Milne- Edwards, " aplatie trausversalement " (in the specimen that lies before me the upper surface of the carapace is broken !). The postfrontal crest shows different characters. When the carapace is looked at from above, the whole upper margin of the orbits, the whole extraorbital tooth, and also that between the latter and the small epibranchial tooth remain visible. The postfrontal crest is somewhat obliquely bent backwards a little beyond the outer angle of the orbits, and unites with the antero-lateral margin, which shows here a very small, granuliform, epibranchial tooth. The extraorbital tooth is larger, slightly concave, obtuse, directed forward, and its outer margin is slightly convex and makes a right angle with the upper margin of the orbits. The distance between the outer angle of the orbits and the epibranchial tooth is proportionately longer than in Potamon fioiveri, namely almost as long as the orbits are broad; the tooth between the outer angle of the orbits and the epibranchial tooth is much longer and has a different shape. This tooth is longer, but lower, less salient than the extraorbital tooth, its outer margin is slightly arcuate and its very short anterior margin measures only one third the length of the outer margin. The granulations of the antero-lateral margin are smaller and less prominent than in the new species from the Soudan. The lower margin of the orbits runs almost transversely in P. fioiveri, but somewhat obliquely upwards in P. aubryi. The sternum of the male is not thickened along the insertion of the chelipedes. The abdomen of the male has a different form. The terminal segment measures only two-thirds of the penultimate, and its length measures two-thirds of the width of its posterior margin. The penultimate segment is, in the specimen of Pot. aubryi lying before me, 9 m m . long, the anterior margin measures 9| mm., the posterior 12 mm., namely the straight line that unites its lateral angles, the margins being concave : the penultimate segment is as long as its anterior margin is broad. The tubercles with which the margins of the meri of the chelipedes are furnished are, in P. aubryi, smaller, less prominent, and the tubercle on the under surface of these joints near the carpal articulation appears as a rounded granule, scarcely larger than those that surround it. The fingers are somewhat shorter in proportion to the length of the palm, and the dactylus is not granulate on its upper margin. The meropodites of the ambulatory legs are a little more enlarged, those of the fifth pair are 20 m m . long and 7| m m . broad; the dactylopodites finally present one spinule more on their posterior margin. Potamon (Potamonautes) pelii Herklots, from the Gold Coast, is also a different species. A young male, type, from the Leydeu Museum, is lying before me. The carapace is much less enlarged: the postfrontal crest runs otherwise, as each half does not extend from the mesogastric suture, transversely outward, but somewhat obliquely backward; the postfrontal ridge, as in P. aubryi, unites |