168 AXEL A. OLSSON 



Length 30.4 mm., height 31.7 mm., semidiameter 1.1 mm. left valve. 



Gorda Bank, Gulf of California in 60 fathoms. Calif. Acad. Sci. 17769. 



Range — Gulf of California to Panama. Mexico: Arena Bank, Gulf of 

 California; Gorda Bank, Gulf of California (Hertlein and Strong); Veragua 

 (Hinds); Gulf of Panama (Dall). Depth of 17 to 182 fathoms. 



Family AMIJSIIDAE 

 Genus AMUSIUM Roeding, 1798 

 Type species by subsequent designation, Herrmannsen, 1846, Ostrea 

 pleuronectes Linne. 



Shell large or small, generally thin, the inflation of the valves usually 

 slight, subequal, the surface without pronounced radial sculpture, often 

 completely smooth and polished. 



Subgenus Amusinm, s.s. 



Shell often large, thin, with rounded disklike valves gaping at both 

 ends. Both valves are smooth and polished, the umbones sometimes weakly 

 ribbed or showing colored rays which may persist on the fossils. Interior 

 of valves showing strong radial riblets or lirae which may be arranged in 

 pairs or singly. 



No known Panamic species. Numerous Miocene species. 



Subgenus CTCLOPECTEN Verrill, 1897 

 Type species by subsequent designation, Pecten pustulosus Verrill. 



Shell small, thin, rounded, scarcely oblique, with symmetrical ears and 

 simple margins. Valves discrepant in sculpture and somewhat in shape, the 

 right valve is a little flattened and upturned at the flexible margin, so as 

 to fit tightly against the left valve; the thin, right valve has in the typical 

 species, regular, thin, elevated, concentrics and its margin is usually flat- 

 tened; the left valve is often marked with weak radials or it may be quite 

 smooth, sometimes carrying radial rows of arched scales, pustules or con- 

 centric lines. No internal lirae. 



This is a group of small, thin-shelled species, with smooth or discrep- 

 antly sculptured valves with simple margins and no internal lirae. Most of 

 the species are deep-water or offshore forms. 



Amusinm (Cyclopecten) pernomiis Hertlein Plate 21, figure 6 



Pecten (Cyclopecten) rotundus Dall, 1908, Bull. Mas. Comp. Zool., vol. 43, No. 6, p. 404. 



Panama Bay in 29 J^ fms.; also at station 2784, in 194 fms. 

 Pecten (Cyclopecten) pernomus Hertlein, 1935, Proc. California Acad. Sci., s«r. 4, vol. 



21, No. 25, p. 320, pi. 18, figs. 11, 12, 13. New name for Pecten (Cyclopecten) 



rotundus Dall, not P. rotundus von Hagenow; Hertlein and Strong, 1946, 



Zoologica, vol. 31, pt. 2, pp. 61, 62. 



Shell very small, thin, white, suborbicular, with subequal ears, both 

 valves nearly equally convex; right valve polished, minutely regularly con- 

 centrically striated, which sculpture is barely visible under a hand lens; 

 posterior ear smooth, anterior finely radially threaded, with a narro\y but 

 clean-cut byssal sulcus and fasciole; left valve finely sharply radially striated, 

 the anterior ear finely reticulated, the posterior apparently nearly smooth; 

 hinge line short, straight; interior smooth, a pair of small auricular crura 

 present; the hinge line with a minute central pit and two relatively large 

 transversely sharply striated, elongate areas representing a permanent 

 provinculum. Height and length, 3; hinge line 2.5; diameter 1.0 mm. 



