8 ALLAN HANCOCK ATLANTIC EXPEDITION REPORT 



5. Chelipeds with high longitudinal ridges, in between which are 



rows of deep pits rugimanus 



Chelipeds with longitudinal rows of large flattened tubercles 6 



6. Fingers of chelipeds not gaping nor full of pubescence; space 



between tubercles of chelipeds glabrous or nearly so; 

 tubercles low, rows irregular .... ackleianus 

 Fingers of major cheliped gaping and full of pubescence; space 

 between tubercles filled with pubescence; tubercles heavy, 

 in regular rows monilifer 



Pachycheles serratus (Benedict) 



Pisosoma serrata Benedict, 1901, p. 135, pi. 3, fig. 7 (type locality, 



Mayaguez, Puerto Rico). 

 Pachycheles serrata ?>chvn\tt, 1935, pp. 184, 185 (part). 



Previous records. — 

 Puerto Rico, Mayaguez: Fish Hawk (Benedict). St. Thomas: 

 (Schmitt). 



Material examined. — 

 A50-39. Bahia Caledonia, Panama; Apr 26, 1939; shore. Icf, l$ov. 

 A57-39. Bahia Caledonia, Panama; Apr 27, 1939; shore. 2<S. 



Measurements. — Males, 5.0 to 5.4 mm; ovigerous female, 6.0 mm. 



Remarks. — Pachycheles serratus is very similar in appearance to 

 P. chacei, described in this paper; the only trenchant difference is the 

 occurrence of seven plates in the telson of the abdomen of P. serratus, 

 and only five in that of P. chacei. This character is not mentioned in 

 Benedict's brief description of Pisosoma serrata or apparent from his 

 illustration of the animal's dorsal surface, and consequently it was 

 difficult to determine whether Benedict's species was the seven- or the 

 five-plated form. According to Dr. Fenner A. Chace, Jr., Benedict's 

 type material cannot be located in the U. S. National Museum's collec- 

 tions. 



Nevertheless, the writer feels that P. serratus can be safely assumed 

 to be the form with the seven-plated telson. This opinion is based on the 

 following characters, derived from Benedict's illustration and/or men- 

 tioned in his description, which apply only to specimens having the seven- 

 plated telson : a, the orbits are deeper and more rounded than in P. 

 chacei; b, the arrangement of the carpal teeth is slightly different; c, 

 the granules in the middle of the carpus are depressed ; d, there is a crest 

 on the manus of both chelipeds ; e, there is no tooth on the cutting edge 

 of the movable dactyl of the major cheliped; /, the walking legs are 



