PANAMIC-PACIFIC PELECYPODA 55 



3. Shell very small, subcircular to subovate, depressed with low umbones. 



N. schencki 



4. Shell larger, plump, strongly inequilateral with high, swollen umbones. 



N. exiqua and N. paytensis 

 II. Ventral margin smooth. 



Subgenus Ennucula 



5. Surface smooth 



N. colofnbtana 



Jfucnla (Nncnla) iphigenia Dall 



Nucula iphigenia Dall, 1895, Proc. U. S. Nat. Museum, vol. 18, No. 1034, p. 15.— Dall, 

 1908, Bull. Mu9. Comp. Zool., vol. 43, No. 6, p. 369, pi. 7, figs. 1, 4.— Hertlein 

 and Strong, 1940, Zoologica, vol. 25, pt. 4, p. 386. 



Shell large (length 30 to 35 mm.), solid, elongate-ovate, the anterior 

 end produced, rounded, the posterior end obliquely truncate. Surface smooth- 

 ish over parts of the shell or with feeble, narrow, irregular concentric 

 wrinkles, strongest on the umbones, crossed by fine, radial striations. Lunula 

 narrow, elongate, the escutcheon small, generally limited by a line from the 

 large posterior area, the margin somewhat projecting or elevated in the 

 middle, smoothish. Interior brilliantly nacreous with a strong pallial line 

 and deeply impressed adductor scars. Hinge with numerous teeth, the 

 anterior set twice as many as the posterior. Ventral margin denticulate. 



Length 35 mm.; height 22.5 mm.; diameter 16 mm. (Dall). 



One of the largest of known Nuculas. Dredged in Panama Bay, off 

 Punta Pinas, in 259 fathoms. A closely related subspecies (N. iphigenia 

 azidensis Olsson* PI. 2, figs. 9, 9a) is common as fossil in the Pliocene of 

 the Burica Peninsula, Panama. 



Nucula (Nucula) decliris Hinds Plate 1, figures 4, 4a 



Nucula declivis Hinds, 1843, Proc. Zool. Soc. London, p. 98. — Hinds, 1844, Zool. Voy. 



Sulphur, Moll., pt. 3, p. 63, pi. 18, fig. 8. (Habitat— ?).—Hanley, 1360, in Sowerby, 



Thes. Conch., vol. 3, Nuculidae, p. 154, pi. 230, fig. 147. 

 Nucula (Nucula) declivis Hindi, Hertlein and Strong, 1940, Zoologica, vol. 25, pt. 4, 



p. 380, pi. 1, figs. 1, 2, 3, 6, 7. 



Shell small (length 5 mm.), solid, inequilateral, the posterior side 

 short, its margin abruptly truncate, relatively convex. Surface smooth with 

 deep, irregularly spaced concentrics and fine radial striation. 



Length 5 mm., height 4 mm., diameter (both valves) 2.9 mm. — (Hert- 

 lein and Strong). 



Nucula declivis was described without indication of locality and because 

 of this and the small size of the original figures, there is some doubt as to its 

 identification. 



Strength of the surface radial striation appears to be variable, de- 

 pending to some extent upon the degree of weathering and wear to which 

 the shell has been exposed. Some of our shells from Ecuador have a smooth 

 surface on which the radial striations hardly show. 



Range — Gulf of California to northern Peru. Ecuador: Manta. Peru: 

 Zorritos. Other records are given by Hertlein and Strong. 

 «0l9son, A. A., 1942, Bull. Amer. Paleont., vol. 27, No. 106, p. 176, pi. 4, figs. 2, 5, 7. 



