6 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 24 



These notations have served as a useful guide in delimiting several 

 species described in this report. One manuscript name proposed by 

 Glassell is adopted herein. 



The writer has seen representatives of every sf)ecies treated ; in most 

 cases long series were available for examination. Many of the earlier 

 descriptions did not contain enough detail to identify a species readily 

 or to distinguish it from its closest relatives; for this reason a de- 

 tailed description has been written for each species (with the exception 

 of the problematical Polyonyx nitidus, which is represented by a diag- 

 nosis only) , using material examined during this study. 



In most cases length-width ratios proved to be of less value taxonom- 

 ically than other characters, and detailed proportional measurements 

 were not taken. The length-width ratio of the carpus is a useful taxon- 

 omic character in members of the genus Petrolisthes, as are several 

 such ratios in Polyonyx. Proportional measurements may prove to be 

 useful in comparative studies of populations of identical or very closely 

 related species from different oceans. For the present study, however, 

 measurements have been largely confined to carapace length, except in 

 the case of the two genera just mentioned ; the size range has been 

 noted for males, non-ovigerous females, and ovigerous females within 

 each species. Carapace and other lengths were measured along the mid- 

 line; widths at the broadest point, excluding spines and lobes. Measure- 

 ments were made with dial calipers and are expressed in millimeters. 



Method of Treatment 



In each species account, information appears under the following 

 headings : 



Synonymy: For species restricted to the eastern Pacific, every 

 known reference is cited. In the case of the few forms occurring in the 

 Atlantic as well, Atlantic references are omitted except those involving 

 original descriptions, designations of type localities, and new combina- 

 tions of names. 



Previous records: Under this heading are listed all Pacific locality 

 records, followed in each case by the collector, if known, and by the 

 author of the reference in parentheses. Localities are arranged in geo- 

 graphical sequence from north to south under several main headings. 

 North-temperate localities are listed under the headings "Alaska," 

 "British Columbia," "Washington," and "California." "Baja California" 

 refers only to localities on the west side of that isthmus ; "Gulf of Cali- 



