184 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



Reinhart, 1943, p. 30), but the type must be examined to settle the 

 question properly. Although Palmer (1951) lists Byssoarca vespertilio 

 (no. 192) as present among the first duplicate series of the Reigen 

 Mazatlan Collection deposited by Carpenter in the New York State 

 Museum in Albany, it has been impossible to locate the sample in the 

 Museum. Byssoarca fusca, reported from Mazatlan by Carpenter 

 (1856a, p. 140), might perhaps be Barbatia lurida also. 



The shells at hand have a white ray radiating from the umbo, 

 similar to that of the Caribbean species Barbatia cancellaria (Lamarck). 

 The periostracum fits the description of Byssoarca vespertilio given by 

 Carpenter (1856a, p. 141), and is soft and lamellose anteriorly. The 

 bristles may be more or less worn off, especially on the median part. 



Small and large eye-spots are present around the whole mantle 

 margin. The posterior part of the mantle margin is especially heavily 

 pigmented. Also pigmented are the foot, the anal region, and the pos- 

 terior part of the gills. The abdominal sense organs are of the same type 

 as those of "Barbatia barbata" (= cancellaria (Lamarck) 1819) 

 (Heath, 1941, PL 5, fig. 10). Measurements of the largest specimen in 

 the present collection (1737-49) are length, 38.6 mm; height, 21.5 mm; 

 diameter, 17.2 mm. 



Occurrence: Rather rarely taken in the intertidal zone down to 12 fms, 

 attached to rocks. 



Distribution : Isla Espiritu Santo, Gulf of California, to Zorritos, Peru 

 (the Peru locality reported by Olsson, 1924). The Galapagos Islands 

 (one valve in the present material). 



Subgenus GUCULLAEARCA Conrad 1865 



Cucullaearca Conrad, Amer. Jour. Conch., vol. 1, 1865, p. 11. 

 Type of subgenus: Byssoarca lima Conrad 1847. (Subsequent designa- 

 tion by Stoliczka, 1871, p. 340) 

 Remarks: The main characters distinguishing this group from Barbatia 

 S.S., according to Reinhart (1935), are a wider ligamental area, larger 

 byssal gape, and posterior enlargement in outline. A posterior enlarge- 

 ment in outline cannot be used as a subgeneric character, as the form is 

 extremely variable. 



According to Heath ( 1941 ), who had only a few species for examin- 

 ation, the anatomy did not show any distinguishing characters between 

 Barbatia s. s. and Cucullaearca. 



