TWO AMPHIPODA OF LUZON 



By C. F. Baker 

 (From the College of Agriculture, Los Banos, P. I.) 



THREE PLATES 



The great, shallow, fresh-water lake of central Luzon, Bay 

 Lake, connected with the sea by Pasig River, possesses a fauna 

 of unusual interest. For example, the curious water snake 

 (Chersydrus granulatus Schneider) is common, and the fisher- 

 men sometimes use its blood to dye their nets. A shark is said 

 to occur in the lake. Its waters possess a marvelously rich 

 plankton and swarm with crustaceans. The bottom is occupied 

 by vast colonies of univalve and bivalve moUusks. Fresh-water 

 sponges are abundant. Finally, under debris along its shores 

 are to be found amphipods and isopods. 



The amphipods found here are of very peculiar interest, for 

 the reason that a few miles distant, at an altitude of 1,060 meters 

 on Mount Maquiling, in the mossy forest, occurs a closely related 

 but very distinct species of the same genus, Parorchestia. 

 Search in streams between these two stations has so far failed to 

 produce amphipods: The beach form lives at water margin, 

 the mountain form under stones in the dripping mossy forest. 

 The beach form has short antennae and fully developed pleopods, 

 while the mountain form has long antennae and reduced pleopods. 

 The heavier armature of the uropods in the mountain form may 

 be an adaptation to the terrestrial life. In form of perion, 

 pleon, and pereiopods, the two species are very much alike. 



These two species are clearly Talitridae by the palpless man- 

 dible and the third uropod of one ramus. Likewise they belong 

 to the genus Parorchestia of Stebbing by the distinct and non- 

 unguiform fourth joint of the palp of the maxillipeds and by 

 the simple two-jointed third uropod. In both species the 

 pleopods decrease very rapidly in size from first to third, though 

 otherwise they are normal. Talitroides of Bonnier, found in a 

 conservatory at Ghent, probably came from some tropical forest, 

 and must be very close to Parorchestia, if not synonymous with it, 

 since in one of our species the pleopods are reduced, though still 

 normal. 



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