COMPLETE HAIG : EASTERN PACIFIC PORCELLANLDAE 59 



tus). In the type description, Glassell (1945) stated that it was taken 

 inside Miraflores Locks during one of their periodic cleanings, and 

 that the water inside these locks varies greatly in saline content. Hilde- 

 brand (1939), who collected zoological specimens (including P. rob- 

 sonae) in Miraflores Locks during the same cleaning period, late March 

 of 1937, reported in more detail on conditions in these locks. When the 

 sea level gates are opened, according to Hildebrand, salinity in the 

 lower chambers is about that of the inner harbor; when water from 

 Gatun Lake enters them, there is about a half and half mixture of 

 harbor and lake water in the lower chambers. Under these adverse con- 

 ditions many animals live in the lower chambers, among them Crus- 

 tacea including P. robsonae. Hildebrand did not find crabs in the upper 

 chambers of Miraflores Locks, where the water is almost fresh. 



Unfortunately, no ecological data accompanied the rest of the known 

 material of P. robsonae: four specimens from Mexico (no specific 

 locality), one from Guayaquil, Ecuador, and five from Panama City 

 reported earlier by the writer (Haig, 1957b). It would be of interest to 

 know whether they were taken under conditions similar to those at the 

 type locality. 



Ovigerous females from the type series were collected in March. 



Relationships: Petrolisthes robsonae is allied to P. armatus 

 (Gibbes), from which it may be distinguished by the presence of two 

 instead of three spines on the carpus of the chelipeds; the reduced 

 number of spines on the merus of the first two pairs of walking legs; 

 and the distinct anterodistal spine on the carpus of the walking legs. 

 The pubescence on the ventral surface of the manus, given by Glassell 

 as a distinguishing character, is indistinct or absent in some specimens. 



Remarks: Among organisms collected in the Miraflores Locks of 

 the Panama Canal, Hildebrand (1939) listed Petrolisthes armatus 

 (Gibbes). These specimens, which were examined by the writer in the 

 U. S. National Museum, proved to belong to P. robsonae. All but one 

 of them were collected on the same day as the type series, which was 

 taken by Elinor D. Robson. 



Also seen was a female specimen (U. S. National Museum Cat. 

 No. 98493) collected by Hildebrand on February 24, 1935, in the 

 lowest channel of Gatun Locks on the Atlantic side of the Isthmus of 

 Panama. This was probably an accidental introduction, for the species 

 has not been reported elsewhere on the Atlantic coast. Its resistance to 



