iiZ AXEL A. GLSSON 



inflated, the posterior side much shorter and depressed. The posterior- 

 dorsal area is small, narrow, a little stronger in the right valve. Surface 

 of valves is concentrically undulated or plicated, the whole overrun by 

 fine, submicroscopic threads, mostly radial and waved. The hinge plate 

 is wide, with a large, downward sloping, and projecting chondrophore in 

 the middle bordered on the anterior side by an inverted V-shaped, cardinal 

 tooth, the inner arm of which projects slightly over the apex of the chron- 

 drophoral pit. The tensilium is small, deeply inset, and attached to a small 

 nymphal plate which roofs over the posterior side of the chondrophore 

 and is fused with the dorsal margin just below the beak. The lateral margins 

 adjacent to the hinge plate are deeply grooved. 



Baeta nndulata (Grould) Plate 56, figures 6-6b 



Lutraria undulata Gould, 1851, Proc. Boston Soc. Nat. Hist., vol. 4, p. 89. — Gould, 



1853, po. cit., vol. 6, pp. 391, 392, pi. IS, fig. 7. 

 Labiosa undulata (Gould), Stearns, 1894, Proc. U.S. Nat. Museum, vol. 17, p. 157. 

 Labiosa {Raeta) undulata (Gould), Dall, 1894, Nautilus, vol. 8, p. 41.— Lamy, 1909, 



Jour, de Conchyl., ser. 4, vol. 11, p. 249. 

 Anatina {Raeta) undulata (Gould), Grant and Gale, 1931, Mem. San Diego Soc. Nat. 



Hist, vol. 1, p. 407, pi. 23, figs. 5a, 5b, 5c. — Hertlein and Strong, 1950, Zoologica, 



vol. 35, pt. 4, pp. 235, 236. — Hertlein and Strong, 1955, Bull. Amer. Mus. Nat. 



Hist., vol. 107, art. 2, p. 205. 



The shell is broadly ovate, with full, median umbones, the small beaks 

 prosogyrate and appressed to the dorsal margin, the anterior side broadly 

 rounded, the posterior side depressed, narrowed and bluntly pointed at 

 the end. Greatest convexity of the valves is over the anterior portion of 

 the umbonal slope. The surface is deeply undulated with narrow concentric 

 riblets, for the most part regular over the midzone, irregular and crowded 

 ventrally. In young specimens with a thin shell, the external undulations 

 are impressed on the inside surface of the valves, less so on older specimens 

 with a heavier shell. 



Length 80 mm., height 64.3 mm., diameter 21 mm. (right valve, Punta 

 Picos, Peru), 



This species seems to be more common along the Peruvian coast than 

 further north, and at times its loose valves appear on the beaches of 

 northern Peru in some numbers. The Peruvian examples also appear to 

 attain a larger size than seen for instance along the coasts of Panama and 

 Ecuador. The most southerly record is Bahia de la Independencia to the 

 south of Paracas, the species hence entering the cold waters of the Peruvian 

 faunal province. 



The West Atlantic R. plicatella (Lamarck) (canaliculata Say) is some- 

 what similar to R. undulata but has the beaks placed nearer the posterior 

 end. 



Range — Southern California to the Bahia de la Independencia, Peru. 

 Panama: Bucaro; Guanico. Ecuador: Galeras; Charapota; Santa Elena. 

 Peru: Tumbez; Punta Picos; Boca Pan; Negritos; Bayovar; Bahia de la 

 Independencia. 



Genus LABIOSA Schmidt in Moller, 1832 



(Anatina Schumacher, 1817 not Bosc, 1816; Cypricia Gray, 1840.) 



Type species by monotypy, Anatina pellucida Schumacher [—Mactra 

 anatina Speng\er=Mactra cyprinus Gray]. Pacific Coast of Mexico and 

 northwestern South America. 



