WILLIAMS: NEW MARINE DECAPOD CRUSTACEANS 



fitting beneath latter; palp conspicuous, flagel- 

 lum densely beset with setae in hollow of curve. 



First maxilliped with lacinia of endopod broad, 

 its distal edge 3-lobed and conspicuously though 

 not heavily setose; oblique mesial margin of 

 strongly advanced anterolateral lobe confluent 

 with broader gradually rounded and much less 

 advanced intermediate lobe, latter in turn fol- 

 lowed by still less advanced tiny mesial lobe, sep- 

 arated by a notch and directed anteromesially; 

 tuft of setae preceding notch. 



Endostome large, divided by low median sagit- 

 tal ridge bifurcated somewhat anteriorly and 

 merging into projecting endostome; each half of 

 palate shallowly concave, crossed by low longitu- 

 dinal ridge slightly offset at its midlength and 

 trending anteromesially from near base of large 

 mandibular palp; ridge flanked laterally by irreg- 

 ular patch of velvety pubescence; smooth lateral 

 2/3 of palate receiving large efferent branchial 

 channels. 



Chelipeds (Figs. 9, 10a, b, c) heavy, subequal; 

 integument punctuate on upper and extensor sur- 

 faces, obscure granulation on upper surfaces of 

 palms and on ridges or raised areas elsewhere; 

 chelae inflated, lower margin of palm arched 

 downward, its rather pronounced keel merging 

 into fixed finger; swollen palm with shallow exca- 

 vation proximally for reception of carpus in flexed 

 position, inner surface glabrous but drawn into 

 moderate and slightly granular elevation slightly 

 in front of proximal excavation. Fingers tan col- 

 ored in preservation (70% ethanol) and darkest 

 proximally, color of fixed finger not extending 

 onto palm; fingers not gaping, prehensile edges 

 entire except for obsolescent proximal tooth on 

 fixed finger of each hand; dactyl longer than rela- 

 tively straight fixed finger, arching down distally 

 to close in distal notch of spooned tip of fixed fin- 

 ger. 



Carpus with extensor surface inflated, right 

 carpus with internal margin rounded, that of left 

 obscurely angled. Merus broadened mesially into 

 cristate flange angled distally for reception of car- 

 pus, strong granules in single line along inner 

 margin, outer surface rounded, strewn with obso- 

 lescent punctations and granules, latter most 

 prominent along distoventral tract. 



Walking legs rather long, flattened, length de- 

 creasing posteriorly in order 3, 2, 1, 4; each with 

 dense patches of short darkened setae inter- 

 spersed with sparer longer setae on extensor sur- 

 face of carpus and propodus (as well as its lateral 

 side on legs 1 and 2), distoventral corner of car- 



pus, and more extensively on dactyl; fifth legs 

 somewhat more flattened than others, propodi 

 relatively broader and not densely setose later- 

 ally. Mean maximum length of propodi about 

 twice width. Dactyls slightly longer than propodi, 

 narrowly lanceolate, shallow longitudinal 

 grooves on anterior and posterior surfaces ob- 

 scured by dense setae, tip stout, corneous. Merus 

 of each with upper margin finely granular, ante- 

 rior lower margin present throughout length but 

 posterior lower margin obsolescent proximally. 



Sternum broadest between legs 1 and 2, nar- 

 rower posteriorly, glabrous beyond outline of ab- 

 domen. 



Abdomen (Fig. lOf) ovate in outline, fully seg- 

 mented and densely fringed with plumose setae; 

 somite 1 slightly arched dorsally to fit contour of 

 adjacent carapace, somites 2-4 of about equal 

 length, somites 5 and 6 progressively longer; ab- 

 domen with greatest width at 4; telson nearly as 

 broad as somite 6, outline broadly arched distally. 

 Somites 2-5 bearing large, well-developed bi- 

 ramous pleopods, outer curved branch lying near 

 edge of abdomen and heavily beset with short 

 setae laterally and mesially, inner branch more 

 sparsely equipped with ovigerous setae and 

 jointed. 



Female openings (Fig. 10^^) large, obscurely 

 subtriangular in outline. 



Color in preservation predominantly off-white 

 except for fingers, matted setal tracts laden with 

 brownish finely particulate matter. 



Remarks. — Brachyuran crabs that resemble 

 Bythograea were observed and reported by Rona 

 et al. (1986). 



Bythograea mesatlantica differs in several re- 

 spects from Pacific members of the genus, 

 B. thermydron Williams (1980) and B. microps de 

 Saint Laurent (1984). Among obvious differences 

 from B. thermydron, the new species has even 

 less ornamentation on the carapace; it lacks a 

 distinct suborbital plate separated by a suture, 

 and the suborbital area is inflated, not flat and 

 inclined; there is a transverse concavity lateral to 

 each eyestalk that terminates near the very dis- 

 tinctive brown spot in the cuticle at either side of 

 the carapace; the eyestalk itself is shorter and 

 thicker than in B. thermydron and the shape and 

 position of the cornea differs. The ischium of the 

 third maxilliped is relatively shorter than in 

 B. thermydron and bears only sparse setiferous 

 punctations on the external surface, it lacks tiny 

 granules on the truncate lobe at the anterolateral 



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