OCR Text |
Show 102 DR. J. G. DE MAN ON A NEW FRESHWATER [Feb. 19, it extends laterally to the antero-lateral margin. The lateral margins of the front, which is strongly deflexed, are very oblique in both males and curve regularly into the anterior margin, which is slightly emarginate in the middle ; the upper surface of the front is finely granular and appears a little concave in the middle. The anterior half of the gastric region is distinctly granulate, and the lateral parts of the upper surface show the usual finely-granulate, transverse ruga?. The rest of the upper surface is smooth and punctate. The suborbital area is finely granulate and separated from the branchial floor, which is covered with short, transverse, granulate ruga?, by a rather shallow groove; this groove, however, is bordered by a finely-granulate line. The pleural suture limiting off the subhepatic and subbranchial regions from the branchiostegite is defined anteriorly by two granulate lines, just as in P. suprasulcatum Hilgd. The outer foot-jaws are furnished with a distinct furrow on the ischium-joint in Hilgendorf's species ; but in the true P. hilgendorfi Pfeffer the "ischial line" is completely wanting, at least in the two males lying before me. The carpus of the anterior legs is covered above with very fine granulate ruga3,and is armed at the inner angle with a conical tooth, beneath which a much smaller one is seen. The immobile finger of the chelipedes shows a deep longitudinal groove a little below the middle of its outer surface, and above this groove still another one that is less deep ; the outer surface of the dactylus is also marked with two longitudinal grooves, the lower of which is, however, rather shallow. Pfeffer describes these furrows as " einen breitern und einen schmalern Langseiudruek." In the species that was described by Hilgendorf there are no furrows on the fingers, at least none on the immobile. One observes on the outer surface of the palm very short, vertical, finely-granulate lines that gradually pass info very fine granules towards and on the fingers. Measurements of the two specimens of Potamon hilgendorfi Pfeffer in millimetres :- o*. " o*. Greatest width of the carapace 26 14 Length of the carapace 19 10.J Distance between the extraorb. angles . . 18| 10| Breadth of the anterior frontal murgin . . 8 4£ Length of the front, in the median line of the cephalothorax 2| 1| Thickness of the carapace 9 5 Breadth of the orbits 5 3 Height of the orbits 3| 1 f Length of the meropodites of the penultimate pair 12 7.1 Breadth of these meropodites 4 2| Length of the meropodites of the fifth Brepaidrt h of these meropodites i4Q$i G2 |