250 University of California Publications in Zoology [Vol. 23 



In case any difficulty is encountered in identifying any of the representatives 

 of this usually puzzling family, the student should consult Miss Eathbun's very 

 excellent monograph covering them (Bull. U. S. Nat. Mus., 97, 1918). The keys 

 here given have been abstracted from it, as well as the original descriptions of 

 recently discovered forms, several plates, a few notes, and remarks. 



Key to the California Genera of the Pinnotheridae 



I. Ischium of external maxillipeds rudimentary or indistinguishably fused with 

 merus, forming a single piece which sometimes lies transversely but usually 

 obliquely across the buccal cavity; palp not more than half as large 

 as merus-ischium. 



A. Carapace suborbicular or subquadrate, not strikingly wider than long. 



Ambulatory legs not successively diminishing in length from first to 

 fourth. 



1. Carapace without two longitudinal, impressed lines leading back 



from the middle of upper margin of orbit. Female larger than 



male and usually ill-calcified. 



Pinnotheres, p. 250. 



2. Carapace with two longitudinal, impressed lines leading back from 



middle of upper margin of orbit. Male unknown. 



Fabia, p. '253. 



B. Carapace much broader than long, anterior margin nearly straight. 



Ambulatory legs diminishing in length from first to last, last very 



small. (Known only from San Pedro.) 



Parapinnixa, p. 255. 



II. Ischium of external maxillipeds usually distinct from merus, though smaller 

 and sometimes imperfectly united with it; palp of good size, usually 

 about as large as merus-ischium. Carapace transverse, usually broadly so. 



A. Carapace much wider than long. Third pair of ambulatory legs the 



longest. 

 1. Third pair of ambulatory legs markedly larger and longer than the 

 others. Carapace more or less membranaceous ; lower, or true 

 anterolateral margin forming an angle with posterolateral margin. 



Pinnixa, p. 255. 

 2. Third pair of ambulatory legs not markedly longer than the others, 

 legs more or less subequal. Carapace hard; lower, or true antero- 

 lateral margin curving gradually into posterolateral margin. 



Scleroplax, p. 267. 



B. Carapace very little wider than long; suborbicular. Ambulatory legs 



more or less subequal, second pair the longest. (Not known north 



of Monterey Bay.) . 



Opisthopus, p. 268. 



Genus Pinnotheres Latreille 



Carapace smooth, more or less membranaceous, sometimes quite hard; sub- 

 orbicular or pentagonal, scarcely wider than long; sometimes a little longer than 

 wide, without longitudinal sulci behind the orbits. Outer maxillipeds oblique; 

 ischium rudimentary; merus large and usually curved; palp three- jointed ; last 

 joint either articulated to inner margin of preceding one, or to its ahtero-external 

 angle. Ambulatory legs subequal, of moderate length; third pair very little if 

 any longer than the others. 



