186 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



In small specimens the ligament is yellowish-brown and is present 

 only posterior to the umbones (PL 11, fig, 5b), while in full grown 

 animals it becomes darker and occupies the entire cardinal area. 



The prodissoconch may be easily seen in small specimens (PI. 11, 

 fig. 9). It is yellow and distinctly set off from the rest of the shell by its 

 color. Its shape is round to triangular, inflated. The hinge line appears 

 to be much shorter than the length of the prodissoconch, but is concealed 

 by the curved, inflated umbones. The surface is granular and indistinct 

 radiating ridges are indicated on the posterior slope. This type of prodis- 

 soconch resembles the figure given by Bernard (1898, PI. 1, fig. 13) of 

 Area sp. He also describes the prodissoconch as yellow (p. 89) and 

 furnished with "ponctuations." 



The anterior mantle margin is furnished with one distinct black 

 pigmented eye-spot on each mantle. 



The largest specimen in the collection measures 94.8 mm in length, 

 58.7 mm in height, and 41.8 mm in diameter. It was obtained by shore 

 collecting at Isla Angel de la Guarda in the Gulf of California (1053- 

 40). 



Occurrence: Usual habitat is under rocks in the intertidal zone. It is 

 occasionally dredged down to 55 fms. 



Distribution: Laguna Manuela, Bahia de Vizcaino, west coast of Baja 

 California, and the Gulf of California, to Zorritos, Peru. The Gala- 

 pagos Islands. Keen (1937) gives its range north to 34° N. Ballast? 



Subgenus CALLOARGA Gray 1857 



Calloarea Gray, Ann. and Mag. Nat. Hist., sen 2, vol. 19, 1857, p. 369, 

 Type of subgenus: Byssoarca alternata Sowerby 1833 (by monotypy). 



Barbatia (Calloarea) alternata (Sowerby) 1833 



Byssoarca alternata Sowerby, Proc. Zool. Soc. London, 1833, p. 17, 

 Fig.: Maury, 1922, PL 2, fig. 11; Reinhart, 1943, PL 11, figs, 5-7. 

 Type loc: Western Colombia; 12 fms; attached to stones on rocky 



bottom. 

 Holotype: British Museum? 



Remarks: Although this is an easily recognized species, very small speci- 

 mens might be difficult to separate from very small specimens of Barbatia 

 (Cucullaearca) reeveana. Barbatia alternata, however, can be distin- 

 guished by the broad, close-set ribs in the middle part of the shell. In 

 small specimens in the material at hand, the prodissoconch is shiny white, 



