226 PROCEEDINGS OF THE ACADEMY OP 



margin ; the first tooth on the upper margin small, situated more 

 directly on the carapax than, and separated from, the following 

 six, which are situated together ; the seventh and eighth separated 

 by a wider si^ace ; last tooth quite small ; apex of the rostrum 

 pointed ; the fifth tooth on the upper margin (counting from the 

 carapax) uearlj^ over the first on the lower margin ; eighth over 

 the last on the lower margin ; those with but six teeth on the 

 inferior margin have the last under the seventh of the superior 

 margin ; the first constant in its situation. Two external flagella 

 of tlie internal anteunfe united for a very short distance, smaller 

 flagellum very short ; all the others very long. First pair of legs 

 short and slender ; carpus more than twice the length of the 

 hand ; fingers half the length of the hand, slightly pubescent ; 

 second pair of legs very long ; carpus not quite as long as the 

 hand ; fingers cylindrical and straight along their approximated 

 surfaces, not as long as the palmar portion of the hand, densely 

 downy ; under surface of this pair of legs covered with spinules to 

 the base of the fingers ; the spinules on the carpus arranged in 

 four parallel rows, of which the anterior and posterior rows contain 

 the largest spinules. Posterior legs rough to the feel, pubescent* 



This species can verja'eadily be distinguished from P. mexicanus 

 (Saussure), which it most closely resembles, by having six or 

 seven teeth on the inferior margin of the rostrum. The carpus 

 in P. mexicanus is longer than the hand, and the terminal segment 

 of the abdomen is armed with three spines. In P. dasydactylus 

 the terminal segment of the abdomen is armed with five spines — 

 one in the middle, and one at either extremity, and a larger articu- 

 lated one on either side of the middle. 



Length from the tip of the rostrum to the end of the terminal 

 segment 4.3*7 inches. 



Habitat. — Tide-water of the Coatzacoalcos River, Isthmus of 

 Tehuantepec. 



PAL^ffiMON SEXDENTATUS, nov. sp. 

 Plate II. Fig. 4-4a. 



Rostrum long and slender, more relaxed than in the preceding 

 species ; longer than the lamelliform appendages of the external 

 antennae ; armed on the superior margin with nine or ten teeth, 

 and six on the inferior margin ; sixth tooth on the upper margin 

 over the first on the lower ; the last on the lower margin half way 



[November 21, 



