412 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 21 



Genus MAGROCOELOMA Miers 



Pericera Milne Edwards, 1834, p. 334 (part). A. Milne Edwards, 



1873b, p. 49. 

 Macrocoeloma Miers, 1879c, p. 665. Rathbun, 1925, p. 463. 



Type: The Atlantic Pisa trispinosa Latreille, 1825, type of Macro- 

 coeloma Miers by original designation. 



Description: Carapace subpyriform or suboblong, but broadened ante- 

 riorly by projecting orbits ; dorsal surface unarmed, or tuberculated, or 

 with a few long spines; margins without a series of elongated lateral 

 spines, but often with a strongly developed lateral epibranchial spine, 

 preceded by some smaller spines. Spines of rostrum well developed. Eyes 

 retractile within roomy, projecting, tubular orbits. Antennae having the 

 basal article considerablv enlarged and armed distally with one or two 

 spines ; the mobile portion sometimes concealed by the rostrum, some- 

 times exposed. Merus of external maxillipeds broader than ischium and 

 notched at internal angle for insertion of palp. 



Chelipeds in the male with the palms enlarged and the fingers either 

 arched and meeting only at tip or in contact throughout. Ambulatory 

 legs rather short. (Rathbun, modified) 



Abdomen with seven separate segments in both sexes. 



Range: From Santa Inez Point, Gulf of California, Mexico, to Bay 



of Guayaquil, Ecuador, in the eastern Pacific. From Cape Fear, North 



Carolina, to Bahia, Brazil, in the western Atlantic. Fiji Islands (A. 



Milne Edwards). Shore to 31 fathoms; in the Atlantic to 163 fathoms. 



Key to the Pacific American Species of Macrocoeloma 

 la. Carapace with fewer than seven spines on posterior half. Ros- 

 trum not deflexed, horns long. Basal antennal spine directed 

 forward or obliquely outward 



2a. Rostral horns subparallel, separated at bases by a narrow 

 interspace. Posterolateral spines acute, directed backward 

 and upward. Four dorsal bosses or tubercles arranged in a 

 diamond. Male first pleopod with an erect, slender keel, tip 



elongate maccullochae 



2b. Rostral horns diverging from bases. Posterolateral spines 

 blunt, directed outward in young specimens, forward in 

 adults. Carapace between posterolateral spines deeply sculp- 

 tured or areolated. Male first pleopod with a bluntly trian- 

 gular keel, tip of moderate length . . . villosum 

 lb. Carapace with seven strong spines on posterior half. Rostrum 

 strongly deflexed, horns short. Basal antennal spine directed 

 downward heptacanthum 



