444 



BULLETIN OF THE BUREAU OP FISHERIES. 



Dr. Rathbun suggests in explanation of this unusual condition of affairs that the habitat of the 

 individual may determine its coloration. The male of this species, as is well known, can move about 

 and doubtless spends more or less of his life swimming from place to place. The young females may, 

 to some extent, have the same habit, and so long as they are free swimming they may be spotted. But 

 as soon as an individual of either sex settles do%vn to a commensal life with some mollusk, it may lose 

 its spots and become uniformly colored. 



The female of P. maculatus alone is common. She is frequently found as a commensal in the shells 

 of Pinna or of Pecten and will probably be found to occur in other lamellibranchs. Occasionally a male 

 will be found in company with a female, more rarely he is found swimming freely in the water. 



Genus DISSODACTYLUS Smith. 



Dissodactylus, S. I. Smith, 1870, p. 172. 

 Echinophitus Rathbun, igoob, p. 590. 



Dissodactylus mellitse (Rathbun). PI. xxxvi, fig. i. 



Echinophilus mellittE Rathbun, 1900b, p. 590. 



Dissodactylus vieltitcE Rathbun, 1901, p. 22: Sumner, 1911, p. 675. 



Carapace about 1.23 as wide as long.oval, smooth, and polished except in the anterolateral portions, 

 where there is a slight pubescence. Front slightly emarginate and fringed with short stiff hairs. From 

 the anterolateral angle a low ridge runs obliquely inward and backward about halfway to the median 

 line. 



Chelipeds short and stout; chela longer than the other articles combined, cylindrical, its upper and 

 outer faces with a few impressed, short, oblique lines from which short appressed hairs extend distally ; 

 fingers considerably shorter than palm, bent inward and curved, their opposable margins with tufts of 

 short bristles ; carpus with a distal fringe of short hairs and an impressed line similar to those on the chela; 

 meros very short and stout, its lower surface with oblique lines. Second, third, and fourth legs stout, 

 their margins fringed with short hairs and their dactyls deeply bifid. Fifth legs with styliform dactyls 

 and fringed with long hairs along both front and.hind margins. 

 Length of a male, 3 mm. ; width, 3.6 mm. 



This minute crab, which, with the exception of Leucifer, is probably the smallest of our malocos- 

 tracan faima, is fairly abundant throughout the region. It is to be found clinging to the spines of the 

 sand dollar (Mellita pentapora), which occurs in great numbers on the shoals and sandy bottoms both 

 within and outside the harbor. In some localities a crab or two will be found on nearly every sand 



dollar examined, but usually they are not 

 present in such numbers. When the sand 

 dollar is lifted from the water, the crabs 

 scurry about over their host and quickly drop 

 off to hide in the sand. 



Genus PARAPINNIXA Holmes. 



Parapinnixa Hohnes, 1895, P- 563. 



Parapinnixa beaufortensis Rathbun. 



Parapinnixa beaufoTtensis Rathbun, 1918, p. 112. 



Carapace rather regularly oval, about one 

 and one-third times as wide as long, with the 

 sm^ace behind the anterior border depressed 

 and plumose ; regions indicated by a series of 

 pits which are light brown in the specimen pre- 

 served in alcohol. Fronto-orbital v.idth two- 

 thirds as great as width of carapace; front about two-fifths width of carapace, a large emargination 

 at its middle in dorsal vie w ; edge of lobes sinuous. A tuft of hair on either side of dorsal surface 

 near lateral margin, but not projecting sideways beyond that margin. A similar tuft, attached to the 

 ventral surface, projects beyond the margin. Eyes large, of a bronze-brown color. 



Fig. 19. — Parapinnixa beaufortensis , dors&X view. Type. cfX2o. 



