No. 10 GARTH : BRACHYURAN FAUNA OF THE GALAPAGOS 391 



803-38. Black Beach, Charles Island, shore, Jan. 23, 1938, 1 female, 



1 young. 

 804-38. Onslow Island, off Charles Island, coral, Jan. 23, 1938, 1 

 young. 



Measure/nents. — Largest female: length 53.7 mm, width 56.6 mm, 

 cheliped 60.0 mm, chela 28.9 mm. 



Color in life. — Frontal, gastric, and cardiac areas, tips of marginal 

 teeth, and spines of carapace pansy purple. Branchial and hepatic regions 

 dahlia purple. Cheliped light brick red at base to pansy purple at ex- 

 tremity; hand Pompeian red, tips of fingers white. Ambulatory legs 

 similar to cheliped ; nail cadmium orange. ( Petersen) 



Habitat. — Rocky shore. 



Depth. — Shore to 6 fms. 



Remarks. — Young individuals are invariably sponge encrusted, some- 

 times so heavily as to be totally unrecognizable. The sponge seems always 

 to be of the same light gray color and delicate texture. Older specimens 

 are completely naked and of the bright shades of red described above. 



A small male from a reef north of Tagus Hill, Albemarle Island, 

 compares in an interesting manner with a specimen of similar size of 

 Mithrax (Mithrax) spinipes (Bell) from San Francisco Island, Gulf of 

 California, Allan Hancock Expedition of 1936. This young male is spinu- 

 lous : the rostral and orbital horns are acute like those of spinipes but are 

 of relatively smaller size. On a key like Rathbun (1925, p. 380), based 

 upon adult characters, the young bellii keys to spinipes. A 17.5 mm speci- 

 men clearly shows the transition from spines to the tubercles and granular 

 pavement of the adult carapace. It is quite possible that a similar transi- 

 tion takes place in the case of spinipes, as indicated in the discussion of 

 that species. However, we do not yet possess specimens of spinipes of size 

 comparable to the tuberculate and granulate adults of bellii; that is, not 

 unless the adults have been given another specific name, such as Mithrax 

 (Mithrax) orcutti Rathbun, of which the young in turn are unknown. 



Mithrax (Mithrax) pygmaeus Bell 



Mithrax pygmaeus Bell, Proc. Zool. Soc. London, vol. 3, p. 172, 1835; 

 Trans. Zool. Soc. London, vol. 2, p. 55, pi. 11, figs. 3, 3f-h, 1836. 

 Mithrax (Mithrax) pygmaeus Rathbun, Bull. 129, U.S. Nat. Mus., p. 

 406, pi. 262, figs. 1-4, 1925. Finnegan, Journ. Linn. Soc. London, 

 Zool., vol. 37, no. 255, p. 624, 1931. 

 Type locality. — Panama, 10 fms, sand. 

 Type. — Not extant. 



Range. — Perlas Islands, Panama (Garman) ; Galapagos Islands 

 (Crossland). 



