56 AXEL A. OLSSON 



Nncnla (Nucnla) exiqna Sowerby Plate 1. figures 2, 2a, 2b, 10, 10a 



Nucula exiqua Sowerby, 1833, Proc. Zool. Soc. London for 1832, p. 198. — Sowerby, 1833, 

 Conch. Illust., Nuculae, p. 6, pi. 16, figs. 24, 24*. — Hanley, 1860, in Sowerby, 

 Thes. Conch., vol. 3, Nuculidae, p. 50. No. 17, pi. 299, fig. 136. 



Nucula (Nucula) exiqua Sowerby, Schenck. 1939, Jour. Paleont, vol. 13, No. 1, p, 36, pi. 

 6, figs. 1-8, 11. — Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, No. 25, 

 p. 381, pi. 1, figs. 4, 5.— Hertlein and Strong, 1955, Bull. Amer. Mus. Nat. Hist., 

 vol. 107, art. 2, p. 169; Palmer, 1958, Mem. Geol. Soc. America, No. 76, p. 61, 

 pi. 1, figs. 6, 7. 



Generally small, length about 6 mm., or less, plump, with high, wide 

 umbones, and with a more or less reticulate surface sculpture formed by 

 strong, fairly wide, concentric riblets and radially threaded interspaces. The 

 radial threads of the interspaces are strongest on the lateral slopes of the 

 shell, sometimes quite indistinct on the umbones. The concentric riblets 

 are generally much stronger than the radial reticulation and on the umbones, 

 the concentric riblets are often close-set, and with smooth summits. The 

 dorsal areas are both well marked, strongly sculptured, each set off sharply 

 by a changed direction of the concentric riblets, the posterior-dorsal area 

 large, cordate, flatly depressed; there is no recognizable lunule within the 

 anterior-dorsal area. Hinge with about 18 teeth in the anterior set and 

 about nine in the posterior. 



A common and widely distributed species, perhaps intergrading with 

 N. paytensis in the border zone. 



Range — Lower California to Peru. Ecuador: Manta; Santa Elena. Peru: 

 Zorritos. 



Nncnla (Nncnla) paytensis A. Adams Plate 1, figures 1, la, lb 



Nucula paytensis A. Adams, 1856, Proc. Zool. Soc. London, p. 51. — Reeve, 1870, Conch. 



Icon., vol. 18, Nucula, pi. 3, fig. 23 Payta, Peru. 

 Nucula crenulata A. Adams, var. Paytensis A. Adams, Hanley, 1860, in Sowerby, Thes. 



Conch., vol. 3, Nuculidae, p. 50, No. 16, pi. 230, figs. 160, 161. 



Like N. exigua but larger, more ovate, less convex, the umbones being 

 less prominent, the sculpture is finer and more uniformly reticulate. Dorsal 

 areas are strongly sculptured. 



Range — Northern Peru. Peru: Paita; Bay of Sechura. 



Nucula (Nucula) schencki Hertlein and Strong Plate 1, figure 6 



Nucula (Nucolopsis) schencki Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, p. 384, 

 pi. 1, figs. 8, 9, 10. 



Shell small (length 2 mm.), thin, polished and rather compressed. Dor- 

 sal margin in front of beaks elevated and broadly rounded, the anterior end 

 more acutely rounded, the posterior and ventral margins broadly rounded. 

 Sculpture is formed by closely spaced concentric riblets crossed by faint 

 radial striation, weakest on the umbones. Dorsal areas weakly defined. In- 

 terior with faint crenulations along the margin, the hinge teeth well developed 

 with nine in the anterior set and five in the posterior. 



Length 2 mm., height \.7 mm., diameter (both valves) 1 mm. — (Hert- 

 lein and Strong). 



Dredged off Port Guatulco, Mexico, in seven fathoms. 

 Range — Mexico. 



Subgenus ENNUCULA Iredale, 1931 

 (Nuculopsis Woodring, 1925. Not Nuculopsis Girty, 1911). 

 Type species by subsequent designation, Singleton, 1932, N. obliqua 

 Lamarck. 



