1921] Schmitt: The Marine Decapod Crustacea of California 217 
II. Carapace usually square or squarish, more or less quadrilateral in outline, 
lateral margins nearly parallel. Frontal region usually broad, bent 
downward, usually without teeth or sharp lobes. Palp of third maxilli- 
peds does not articulate at or near the inner angle of the merus. Position 
of male genital openings peculiar since they lie upon the sternum and 
are connected with the copulatory appendages on the abdomen by means 
of furrows excavated in the sternum. 
A. Small commensal or symbiotic crabs with front, orbits and eye-stalks 
usually very small. Carapace often more or less membranaceous, 
frequently more or less rounded. F ; 
Pinnotheridae, p. 249. 
B. Free-living crabs, with front, orbits, and eye-stalks not especially re- 
duced. Carapace hard and firm, lateral margins either strictly 
parallel or only slightly arched. 
1. Third maxillipeds with more or less of a gap left between them. 
Front usually markedly wide, eye-stalks of moderate size. Dac- 
tyls of ambulatory legs compressed, and armed with strong 
spines. The base of the abdomen in the male usually covers the 
whole width of the last thoracic sternum. ; 
Grapsidae, p. 269. 
2. Third maxillipeds almost or quite close to the mouth. Front mod- 
erately or very narrow; orbits transversely lengthened, eye-stalks 
usually very long. Dactyls of ambulatory legs styliform and 
devoid of spines. The base of the abdomen usually does not cover 
the whole width of the last thoracic sternum between the last 
ir of legs. 
pair of legs Ocypodidae, p. 277. 
Family CaNncripAE 
Carapace broadly oval, front. with several teeth, one of which is median. 
Antennules fold back longitudinally. Antennal flagella usually short and more 
or less hairy. Third maxillipeds overlapping endostome. 
Genus Cancer Linnaeus 
Carapace transverse, subelliptical, often indistinctly areolated; front narrow, 
cut into five teeth or lobes. Eye-stalks. short; orbits small, with two fissures in 
both upper and lower margins. Basal antennal joint usually somewhat enlarged 
and united with the front, thus excluding the flagellum from the orbit. 
KryY TO THE CALIFORNIA SPECIES OF CANCER 
(For key to the California specimens of Cancer 20 mm. and less in width 
see p. 219) 
I. Anterolateral and posterolateral margins meeting at a distinct angle; cara- 
pace widest at ninth or tenth (sometimes eighth) tooth; nine, ten or 
eleven teeth. 
A. Front markedly produced beyond outer orbital angles, forming five sub- 
equal teeth. Fingers of chelipeds dark-tipped. 
productus, p. 220. 
