80 AXEL A. OLSSON 



lets, noded or cancellated by the concentrics. The periostracum is profuse, 

 pilose and dark-colored, the color of the shell underneath being white or 

 brownish. Hinge line long and straight, with numerous small teeth, the 

 posterior set being much the longer, the distal members enlarged and set 

 obliquely. 



Two subgenera are regional. 



I. The shell is fairly regular in shape, the color of the surface below the 

 periostracum brownish. Sculpture is formed by small, radial, threadlike 

 riblets, the smaller spaced between larger ones so that the pattern 

 appears rayed. Cardinal area is low and narrow, the ligamental grooves 

 few in number. 



Subgenus Barbatia, s.s. 



II. Shell generally much distorted, the ventral margin deeply sinuated by 

 a large, open, byssal gap. Color of shell beneath the periostracum is 

 white. Sculpture formed by rather coarse, beaded, radial riblets, not 

 in rayed pattern. Cardinal area is generally quite high and closely 

 covered with tent-shaped ligamental grooves. 



Subgenus Cucullaearca 



Barbatia (Barbatia) lurida (Sowerby) Plate 6, figure 4 



Byssoarca lurida Sowerby, 1833, Proc. Zool. Soc. London, p. 19 Santa Elena, Ecuador. 



Area lurida Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 14, fig. 95. 



Barbatia (Barbatia) lurida (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, 



p. i74._Rost, 1955, Allan Hancock Pacific Expeditions, vol. 20, No. 2, pp. 



182-184, pi. 11, figs. 3 a-b; text figs. 81 a-c. 

 Byssoarca vespertilio Carpenter, 1856, Cat. Mazatlan Shells, Brit. Mus. p. 140. No. 



192, Mazatlan, Mexico. 

 Barbatia (Barbatia) vespertilio (Carpenter), Maury, 1922, op. cit., pp. 174, 175. 



Shell small or of medium size, obliquely oblong, convexly humped, 

 highest along the posterior-umbonal slope, the anterior side somewhat 

 narrower than the posterior. Umbones are wide and full, sometimes slightly 

 sulcated. The sculpture is similar to that of B. barbata, being composed 

 of small, threadlike radials, the posterior set interspersed with larger or 

 deeper ones so as to give a banded or rayed appearance. Color dark-brown 

 on the posterior half and a lighter brown on the anterior. The hinge line 

 is shorter than the full length of the shell, the teeth small in the middle zone, 

 the distal members much larger. Interior white in the anterior section, 

 brown in the posterior, the anterior-ventral margin sinuated by the byssal 



gap- 



Although B. lurida and B. vespertilio are here placed together as a 

 single species, fresh specimens with the periostracum intact may show them 

 to be distinct. Worn beach specimens of B. lurida from Santa Elena, Ecuador, 

 and northwestern Peru, have a slightly distorted shell with the beaks 

 placed a little in front of the middle and the posterior-umbonal slope is 

 higher and more convex. The cardinal area is like that of B. barbata of 

 Europe and generally covered completely with strong ligamental grooves 

 on both sides of the beaks. The sculpture is rayed. The type of B. vespertilio 

 examined at the British Museum is a perfect specimen, covered with perio- 

 stracum, and the two valves spread open and glued onto a glass plate; its 

 dimensions are: length 33.5 mm., height 16 mm. 



