1921] Schmitt: The Marine Decapod Crustacea of California 147 
A. Carapace not spiny on upper surface; rostrum short, simple, triangular. 
1. Carapace and legs much flattened and more or less hairy or pubescent ; 
lateral margins of carapace with a few small teeth or spines. 
Anterior margin of ambulatory legs deeply incised, incisions 
hidden by hairiness of legs. (Not known south of Monterey.) 
Hapalogaster, p. 148. 
2. Carapace not so flattened, moderately convex, somewhat roughened, 
granular on upper surface, slightly setose but not hairy; lateral 
margins unarmed. Ambulatory legs subeylindrical, very sparsely 
haired. (Not known south of Pacific Grove.) 
Oedignathus, p. 150. 
B. Carapace distinctly flattened and covered with numerous subequal 
spines; rostrum terminated by strong spines. Legs spiny, with long 
hairs arising from tip of spines. (Not known south of Monterey.) 
Acantholithodes, p. 152. 
II. Abdomen segmented, and subdivided into more or less well calcified plates, 
which are usually applied quite closely to the thoracic sternum; basal 
(second) segment always provided with a pair of marginal and a pair 
of lateral plates, and a median plate; plates either separated by sutures 
or more or less completely fused with one another; abdomen quite 
smooth or armed with more or less prominent tubercles or spines; occa- 
sionally abdominal plates have a central membranous area. 
A. Abdominal plates with characteristic raised and rounded papillated 
edges enclosing a central membranous area; median and lateral 
plates of basal (second) segment distinct. Ambulatory legs about 
as long as greatest width of carapace. Outline of carapace prac- 
tically forming an equilateral triangle; upper surface with two deep 
pits within a triangular excavated area, surrounded by rounded 
papillated tubercles. (Not known south .of Monterey.) 
Phyllolithodes, p. 153. 
B. Abdominal plates without a central membranous area. 
1. Ambulatory legs shorter than the greatest width of the carapace, 
usually much shorter. 
a. Carapace broadly oval, convex, smooth, and produced into lateral 
expansions, which completely conceal the ambulatory legs, 
forming a large expanded dorsal shield. Basal (second) 
abdominal segment entire. (Not known south of Monterey.) 
Cryptolithodes, p. 154. 
b. Carapace not so produced, more crab-like in appearance, more or 
less prominently tuberculated. 
i. Outline of carapace practically forming an equilateral tri- 
angle; with a deep semilunar fossa separating the smooth 
hemispherical cardiac region from the other more or less 
eoarsely tubereulated regions of the carapace. Plates of 
basal (second) abdominal segment distinct. (Not known 
south of Crescent City.) Rhinolithodes, p. 157 
ii. Outline of carapace roughly pentagonal or hexagonal, very | 
convex, roughened, with many close set, short tubercles 
and fewer more or less prominent subconical tubercles. 
Basal (second) abdominal segment entire. (Not known 
south of Monterey. 
om y-) Lopholithodes, p. 155. 
