364 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 21 



Remarks: The decision to reduce Mithrax (Mithrax) clarionensis 

 from a full species to a subspecies and to relate it to M. (M.) sinensis 

 is the result of pleopod studies. As will be seen by a comparison of Plate 

 V, figures 5 and 6, the male first pleopod of the two forms is identical. 

 Retention of clarionensis as a geographical race appears justified on the 

 basis of the general characters indicated in the diagnosis and description 

 above, which are clear-cut, and because the two forms, in view of the 

 isolation of Clarion Island from the mainland, do not interbreed, although 

 they may potentially be able to do so. 



Mithrax (Mithrax) pygmaeus Bell 

 Plate V, Fig. 7; Plate 41, Fig. 4 



Mithrax pygmaeus Bell, 1835b, p. 172; 1836, p. 55, pi. 11, figs. 3, 3f-h. 

 A. Milne Edwards, 1875, p. 104. Miers, 1886, p. 86. Rathbun, 

 1910, p. 574. Finnegan, 1931, p. 624. Crane, 1947, p. 73. 

 Mithrax (Mithrax) pygmaeus, Rathbun, 1925, p. 406, pi. 262, figs. 

 1-4. Garth, 1946, p. 391 ; 1948, p. 29. 



Types: Two males, cotypes, the measured cotype 6.4 mm in length 

 and width, originally deposited in the Museum of the Zoological Society 

 [London] and the Bell Museum, no longer extant. 



Type locality: Panama, 10 fathoms, sand; Hugh Cuming, collector. 



Localities subsequently reported, with collectors: Costa Rica: Port 

 Parker and Port [Puerto] Culebra, Zaca (Crane). Panama: Taboga 

 Island, St. George (Finnegan) ; Perlas Islands: S. W. Garman (Rath- 

 bun, 1925), Contadora and Saboga Islands, Askoy (Garth, 1948). 

 Colombia: Utria Bay [Port Utria] and Gorgona Island, Askoy 

 (Garth). Ecuador: Galapagos Islands, St. George (Finnegan) ; off 

 Esmeraldas, Askoy (Garth). 



Atlantic analogue: None. A Bay of Panama endemic species. 



Diagnosis: Rostral lobes short and broad, subarcuate to subtruncate. 

 Anterolateral spines in two rows, with the inner containing about six, 

 the outer about nine. Basal antennal article broad, two marginal teeth. 

 Chelipeds and ambulatory legs, especially in male, greatly elongated. 

 Antennal flagellum long and slender. Male first pleopod with a pointed tip 

 and a subterminal swelling. A small species. 



Description: Carapace depressed, subovate, regions rather distinct, 

 surface smooth, lateral margin armed with two rows of spines, the upper 

 row of six beginning at the outer orbital angle, the outer row of about 

 nine, partly submarginal, beginning at the lower orbital tooth and meet- 

 ing the first row at the posterolateral angle. Frontal lobes short, broad* 



