COMPLETE HAIG : EASTERN PACIFIC PORCELLANIDAE 23 



presence of conical tubercles on the anterior margin of the carpus and 

 a thick fringe of hairs on the outer margin of the manus, and by the 

 shape of the fingers, which differs markedly in the two chelipeds. The 

 basal segment of the antennule is much like that of some members of 

 the P. violaceus group of species, discussed below. 



A well-marked group ("Gruppe des Petrolisthes tuberculatus" of 

 Ortmann) contains two species confined to Peru and Chile, Petro- 

 listhes tuberculatus (Guerin) and P. tuberculosus (H. Milne Edwards). 

 They are characterized by the strongly trilobate front; two narrow, 

 strongly projecting lobes on the basal segment of the antennule (see 

 text-fig. 3) ; and a row of uneven, serrate teeth on the anterior margin 

 of the carpus. These two species are particularly distinctive, and to- 

 gether should probably form a separate genus or subgenus. 



One large group consists of species in which the carpus of the 

 cheliped is not armed with teeth or spines (except for minute spinules 

 in the young of some forms), and in which there are no spines on the 

 carapace and walking legs. The basal antennular article is variable. 

 The type species of the genus, Petrolisthes violaceus (Guerin), belongs 

 here but is somewhat aberrant in that the orbits are nearly straight in- 

 stead of concave. Other aberrant forms are P. rathbunae Schmitt, which 

 has piliferous striations on the carapace, and the posterodistal angle 

 of the merus of walking leg 1 very slightly produced into a spine; and 

 P. tiburonensis Glassell, which is sexually dimorphic and has rows of 

 nodulate tubercles along the anterior margins of the walking legs. This 

 group is almost entirely confined to the eastern Pacific, where it is 

 represented by 17 tropical and temperate species; P. quadratus Benedict, 

 1901, occurs in the western Atlantic. In another group of species closely 

 allied to these, there is a single tooth or small lobe at the proximal end 

 of the anterior margin of the carpus; included are P. elongatus (H. 

 Milne Edwards), 1837, from New Zealand and southern Australia, and 

 such Indo-Pacific forms as P. unilobatus Henderson, 1888, P. japon- 

 icus (de Haan), 1849, and P. inermis Haswell, 1882. 



The final natural division among eastern Pacific Petrolisthes con- 

 sists of species in which the hepatic and protogastric lobes are usually 

 strongly accentuated; the front is trilobate and usually sharply de- 

 flexed; the carpus is usually short and stout; and the carpus and 

 manus usually bear longitudinal crests and grooves. Nobili (1901, pp. 

 17-18) recognized and discussed the relationship of the forms known to 

 him. Included are a western Atlantic species, Petrolisthes jugosus 



