72 AXEL A. OLSSON 



Genus KUCOELLA Wood, 1851 



Pleurodon Wood, 1840, not of Harlan, 1831 (Mammalia); Nuculina 

 d'Orbigny, 1844, not of "Felippi" Porro, 1837; Cyrillona Iredale, 1829; 

 Neopleurodon Hertlein and Strong, 1940. (See Vokes, 1956, Jour. Paleont., 

 vol. 30, No. 3, pp. 652.) 



Type species by monotypy, Pleurodon ovalis Wood. 



The shell is usually small, resembling Nucula but with a non-nacreous 

 structure, its shape oval, subtrigonal to obliquely egg-shaped, the anterior 

 side being shorter and more sharply descending, the posterior side hence 

 longer and often a little expanded. Hinge plate relatively short and wide, 

 somewhat angulated under the beak, in the angle of which lies a small 

 resilifer, bordered on each side by a few, relatively large teeth; the left 

 valve has a prominent, posterior lateral tooth which is received in a de- 

 pression in the opposite valve. Surface smooth or with fine concentrics. 



There is some uncertainty as to the orientation of the valves of 

 Nucinella (see Vokes, p. 656) which must await fuller knowledge of the 

 internal anatomy and the study of the ligament from fresh specimens. Vokes 

 considered the ligament as external, Dall and some other authors as internal. 

 In the above description, I have considered the ligament as being internal 

 and the shorter side as anterior. 



Nucinella subdolns (Strong and Hertlein) Plate 17, figure 12 



Pleurodon subdolus Strong and Hertlein, 1937, Proc. California Acad. Sci., 4th ser., vol. 



22, No. 6, p. 162, pi. 35, figs. 14, 18, 19. About 5 miles west of Mazatlan, 



Mexico, 12 fra. 

 Cyrilla (Neopleurodon) subdolus (Strong and Hertkin), 1940, Zoologica, vol. 25, pt. 



4, p. 420. 

 Nucinella subdolus (Strong and Hertlein), Vokes, 1956, Jour. Paleont, vol. 30, No. 3, 



p. 666. 



Shell minute, obliquely ovate, smooth, white, translucent; beaks 

 prominent, hinge line short, straight, forming a small, flaring projection at 

 each end; hinge plate broad, continued as a shelf along more than half of 

 the posterior side of each valve, the inner margin turned up and, in the 

 left valve, ending in a lateral tooth; cardinal teeth small, indistinct, divided 

 into a posterior and anterior series, three or four in each, which meet at 

 an angle, those in the posterior series being larger and wider spaced. The 

 type measures: length 1.85 mm., height 2.5 mm. — [Strong and Hertlein, 

 1937]. 



Although known from only a few specimens dredged off Mazatlan, 

 Mexico, this small species may prove to have a wide distribution through 

 the Panamic Province. A few imperfect specimens, probably this species, 

 are known from the Pliocene of Quebrada Camarones, Ecuador, Nucinella 

 adamsi (Dall) from the Florida Straits is a similar species. 



