222 AXEL A. OLSSON 



Like Anodontia, s.s. in shape, rounded, and spherical, but with the 

 dorsal areas well defined and deeply impressed. 



ADOdontia (Lissosptaaira) spherica (Dali and Ochsner) Plate 30, figure 2 



Lucina sPherica Dall and Ochsner, 1928, Proc. California Acad. Sci., ser. 4, vol. 17, Nos. 



4, 5, pp. 121, 122, pi. 3, fig. 8 ; pi. 4, figs. 2, 7 "Pliocene. Indefatigable Island, 



Galapagos". 

 Loripinus (Pegophysema) spherica (Dall and Ochsner), Pilsbry and Olsson, 19+1, Proc 



Acad. Nat. Sci. Philadelphia, vol. 93, p. 57. 



Shell of medium size (length 58 mm.), suborbicular, the height and 

 length nearly equal, moderately convex and moderately heavy. Surface 

 smoothish or roughened by irregular, concentric lines of growth. Lunule 

 narrow and deep, confined mostly to the right valve. The beaks are placed 

 a little nearer the anterior end and face forward over the anterior submar- 

 gin which is somewhat depressed, arcuate, and semilunate in shape. Dorsal 

 areas well defined, depressed, the posterior one longer and more strongly 

 set off from the disk. Shell cavity deep, smooth or radially striated, 

 or granulose within the paUial line. 



Easily separated from A. edenttdoides by its less inflated valves and 

 deeply impressed posterior-dorsal area. 



This species was first described as a Pliocene fossil from the Galapagos 

 Islands. It is also a common shell of the Pliocene of Punta Blanca, Ecuador, 

 where it is the dominant fossil in some beds. As a Recent species, it appears 

 to be rare. I have a single, much decayed specimen from Isla del Gallo, 

 Colombia, and there is a small shell in the U.S. National Museum collection, 

 (USNM 96398) from Lower California. 



Range — Lower California to Ecuador. Colombia: Isla del Gallo. 



1 Superfamily CHA3IACEA 



Family CHAMIDAE 



Shell irregularly suborbicular, attached (at least in the early stages) by 

 the anterior side of one valve. In the temporarily fixed forms, such as 

 Echinochcmui, the valves are similar in shape and sculpture, and the attach- 

 ment scar (on the right valve) is comparatively small. Permanently fixed 

 forms have strongly unequal valves; the lower or attached valve is then 

 much larger and deeper while the upper or free valve is small, depressed, 

 and caplike. Shells are normally heavy and thick walled, composed of two 

 contrasting layers, the outer is prismatic in structure and often highly 

 colored, and it generally shows as a band around the inner ventral margins 

 of the valves; the inner layer is porcellaneous. In the dextral Chamas, the 

 hinge has a large, massive, central cardinal tooth, often strongly rugose in 

 the right valve which fits into a socket in the left; in the sinistral forms, 

 the hinge arrangement is reversed. The external sculpture is often elaborate 

 formed by both radial and concentric elements, often foliaceous or spini- 

 ferous. Adductor scars are large, elongate, connected by a simple, entire 

 pallial line. 



Carefully cleaned and in good condition, the shells of the Chamidae 

 include some of the most colorful marine bivalves, often rivaling Spondylus 

 in beauty, but old shells long exposed to erosive wave action and deeply 



