22 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 24 



Remarks: A few of the more aberrant eastern Pacific species for- 

 merly included in Petrolisthes are assigned in this report to three new 

 genera, Ltopetrolisthes, Allopetrolisthes, and Clastotoechus. Petrocheles 

 Miers, 1876, which contains one species each from New Zealand and 

 southern Australia, was originally described as a subgenus of Petro- 

 listhes but is usually considered to be a full genus. Glassell (1945, p. 

 229) noted that the western Atlantic species Petrolisthes tortugensis 

 Glassell, 1945, resembles Petrocheles in some respects; however, the 

 present writer, who has compared specimens of Petrolisthes tortugensis 

 and Petrocheles spinosus (Miers), 1876, considers Glassell's species 

 generically distinct from both Petrolisthes and Petrocheles. 



With the above forms excluded, the genus is composed of perhaps 

 75 or more species, with 39 recognized from the eastern Pacific alone. 

 The species tend to fall into several natural groups, some of which 

 were discussed by Ortmann (1897, p. 275 et seq.). The interrelation- 

 ships of the species are not at all clear, however, and it seems inad- 

 visable to attempt any splitting of the genus until it can be studied on 

 a worldwide basis. 



One large group of species is characterized by the presence of teeth 

 or spines on the anterior margin of the carpus, and one or two postero- 

 distal spines on the merus of walking leg 1 ; in addition there may be 

 any or all of the following: epibranchial and supraorbital spines; a 

 row of spines on the outer margin of the manus and on the anterior 

 margin of the walking legs; and spines on the frontal, orbital, and 

 lateral margins of the carapace. The anterior margin of the basal anten- 

 nular article usually bears two or more spines. Many of these species 

 have transverse piliferous striations on the carapace. This group, which 

 corresponds to the divisions called "Gruppe des Petrolisthes gala- 

 thinus" and "Gruppe des Petrolisthes lamarcki" by Ortmann (1897), 

 contains a dozen eastern Pacific species. Related forms are Petrolisthes 

 politus (Gray), 1831, and P. amoenus (Guerin), 1855, from the west- 

 ern Atlantic; P. cessacii (A. Milne Edwards), 1878, and P. monodt 

 Chace, 1956, from the eastern Atlantic; and a number of Indo-Pacific 

 species, among them P. lamarckii and P. asiaticus (Leach), 1820, P. 

 militaris (Heller), 1862, P. coccineiis (Owen), 1839, and P. decacan- 

 thus Ortmann, 1897. 



Petrolisthes hirtipes Lockington and P. nigrunguiculatus Glassell, 

 which are almost entirely restricted to the Gulf of California, are not 

 closely related to any other species. They are characterized by the 



