PANAMIC-PACIFIC PELECYPODA 33$ 



Shell small or of medium size, thin, white, subovate, moderately in- 

 flated over the wide, umbonal region, the posterior side shorter, depressed, 

 flaring somewhat at the dorsal corner, the end widely gaping. The pos- 

 terior-dorsal area is defined by an elevated ridge running downward from 

 the beak. Hinge as in Raeta, the chondrophore large, the external section 

 of the ligament small. Surface of valves smooth except for irregular lines 

 of growth and sometimes small, obscure undulations on the umbones; there 

 are no submicroscopic markings as in Raeta. The paHial sinus is short and 

 high not confluent with the pallial line below. 



An earlier paper by Schmidt (1829, Vers. Einth. Conch., reported in 

 Sherborn), in which the name Labiosa may have been used, has not been 

 seen. In Moller, 1832 (Isis, p. 130), Anatina Schumacher is noted in the 

 synonym of Labiosa, hence, it may be considered a replacement name for 

 Anatina and would have the same type species. 



This is the Anatina Schumacher, 1817, unfortunately preoccuppied by 

 B'osc, 1816. The genus Labiosa has often been enlarged to include Raeta 

 which is fully distinct, differing in shape, absence of strong undulations, 

 and minute, submicroscopic, radial markings. 



Labiosa anatina (Spengler) Plate 57, figures 3, 3a 



Mactra anatina Spengler, 1802, Skrivl. Naturh. Selsk., vol. 5, pt. 2, p. 120. 



Anatina pellucida Schumacher, 1817, Nouv. Syst. Hab. Vers Test., p. 126, pi. 8, fig. 1. 



Mactra cyprinus Gray, 1828, in Wood Index Testae. Suppl., pi. 1, fig. 1. — Gray, 1854, 



Conch. Icon., vol. 8, Mactra, pi. 10, fig. 37. 

 Cypricia anatina (Spengler), Gray, 1847, Proc. Zool. Soc. London, p. 185. 

 Labiosa anatina (Spengler), Dall, 1894, Nautilus, vol. 8, No. 4, p. 41. West Mexico. — 



Lamy, 1917, Jour, de Conchyl., vol. 63, pp. 349, 350. 



This species is similar to the West Atlantic L. lineata (Say) but its 

 outline is more ovate, the beaks are more centrally located, the anterior- 

 dorsal margin less descending, and the posterior-dorsal area wider, its 

 margin more rounded and flaring. A broken flat valve measures: length 

 41.8 mm., height 28.3 mm., diameter 8 mm. Santa Elena, Ecuador. 



Range — Coast of Mexico southward to Ecuador. Ecuador: Santa Elena. 



Genus TUSIBEZICONCHA Pilsbry and Olsson, 1935 



Type species by original designation, Mactra thracoides Adams and 

 Reeve.^2 



The shell is small, thin, white, ovate, the anterior side short and more 

 convex, the posterior side longer and depressed. Whole surface of shell is 

 covered with narrow, deep undulations, concentric to the valve margin on 

 the anterior side, oblique to it on the posterior, thus producing the appear- 

 ance of a broken or damaged valve. In addition the whole surface is covered 

 with irregular lines of growth producing wrinkles as if painted with a coarse- 

 haired brush. Posterior-dorsal area not defined. Hinge much like Mactrel- 

 lona; the tensilium seated on a small, shelly plate behind the beak and 

 above the deep chondrophore. Mostly on mud flats or similar locations. 



Tnmbeziconcha thracoides (Adams and Reeve) Plate 56, figure 3 



Mactra thracoides Adams and Reeve, 1848, Zool. Voy. Samarang, Moll., p. 81, pi. 23, 

 fig. 8 "Eastern Seas". — Reeve, 1854, Conch. Icon., vol. 8, Mactra, pi. 20, 

 fig. 116. 



ispilsbry, H. A., and Olsson, A.A., 1935, The Nautilus, vol. 48, No. 4, pi. 6, fig. 9. 



