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 Rathbun’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. 
Kry 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.) oe. 
Parapinniaxa, 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. 
Pinniza, 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 sulei 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 antero-external 
angle. Ambulatory legs subequal, of moderate length; third pair very little if 
any longer than the others. 
