from May to November in North Carolina, and 

 have been found along the Potomac River in Jan- 

 uary (U.S. National Museum records). Hyman 

 (1924b) briefly described the first zoeal stage. 

 Costlow and Bookhout (1960) described 4 zoeal 

 stages and 1 megalops stage from 1,200 zoeae 

 reared on Artemia nauplii and Arbacia eggs under 

 constant conditions of temperature, salinity, and 

 light. Costlow, Bookhout, and Monroe (I960) 

 found that optimum salinities exist for each larval 

 stage, but that development proceeds best in 

 the 20-26.7 °/oo range (among those tested). 

 Temperature was found to have more effect on 

 length of larval development than on mortality, 

 with higher temperature speeding development. 

 No "extra stages" were observed. The authors 

 concluded that salinity is the chief physical factor 

 confining S. cinereum to estuaries. 



Pearse (1929) found that this species can sur- 

 vive for a considerable period of time in dilutions 

 of sea water and also that it shows considerable 

 resistance to desiccation. Oler (1941) maintained 

 captive specimens from a Maryland tidal river in 

 a house basement for about a year. The animals 

 burrowed in mud in an aquarium where the only 

 moisture provided was tap water. Vegetable mat- 

 ter was fed at irregular intervals. After several 

 months, the larger animals ate the smaller ones, 

 presumably at the time of ecdysis. Duncker 

 (1934), in Germany, secured three live female S. 

 cinereum which had been transported by chance in 

 a cargo of logs from the West Indies. The animals 

 were kept alive in a glass jar with damp peat and 

 a container for a source of fresh water. One lived 

 4 years and 72 days from date of captivity. The 

 crabs were fed shredded beef or fish and commer- 

 cial fish food plus Collembola that appeared in the 

 jar. All eating was done on land. Some regen- 

 eration of lost appendages occurred, and the long- 

 est lived specimen molted four times, molting al- 

 ways taking place in water. To the author's 

 surprise, eggs were released six times, always in 

 water, the longest lived female producing five of 

 these batches. Larvae hatched from all but one 

 of the egg masses, but survived only a short time. 

 Duncker concluded that one mating was effective 

 for 3 years or more. The incubation period was 

 approximately 30 days. The female ate eggs that 

 protruded over the edge of the abdomen. The 

 number of eggs ranged from about 4,700 to 13,400 



per sponge. Duncker considered that S. cinereum 

 acted more like a land animal than a water- 

 inhabiting animal, each individual having its own 

 burrow. 



Teal (1959) implied the same conclusion, for 

 in experiments under water this species was rel- 

 atively inactive, thus holding its oxygen con- 

 sumption down. There was some experimental 

 evidence for thermal acclimation of metabolism, 

 but more evidence for acclimation by selection 

 of microclimate. Gray (1957) also emphasized 

 the terrestrial habits of the species, but showed 

 that its relative gill area is nearly double that of 

 the similar species Ocypode quadrata. 



Subfamily Plagusiinae 



Front cut into lobes or teeth by antennular 

 clefts visible in dorsal view. Lower border of orbit 

 curving down into line with prominent anterior 

 border of buccal cavity. External maxillipeds 

 neither completely closing buccal cavity nor leav- 

 ing wide rhomboidal gap, not crossed by an 

 oblique hairy crest ; palp articulating near antero- 

 external angle of merus, often no flagellum on 

 exposed exognath. Antennal flagella short. Male 

 abdomen filling all space between last pair of legs 

 (Rathbun, 1918b.). 



Genus Plagusia Latreille, 1804 



Rathbun, 1918b, p. 331.— Monod, 195G. p. 455. 



Plagusia depressa (Fabricius) 



Figure 207 



Cancer depressus Fabricius, 1775, p. 406. 



Plagusia depressa: Rathbun, 1918b, p. 332, text-fig. 154, pi. 101 

 (rev.).— Monod, 1956, p. 455, figs. 614-617 (rev.). 



Recognition characters. — Carapace subhexag- 

 onal, wider than long, depressed, covered with 

 flattened tubercles margined with short setae. 

 Regions distinct; front of gastric region with a 

 series of approximately six, prominent, acute tu- 

 bercles arranged in an arc. Indefinite front broad, 

 with a deep median furrow and deep notches for 

 antennules ; a spinif orm tubercle on each side be- 

 tween median furrow and antennulary notch. 

 Orbits deep; outer orbital angle produced into a 

 strong, curved spine followed on anterolateral 

 margin by three similar spines of diminishing 

 size. Epistome prominent beyond anterior border 

 of carapace and usually cut into five lobes. 



MARINE DECAPOD CRUSTACEANS OF THE CAROLINAS 



223 



