PANAMIC-PACIFIC PELECYPODA 153 



Figured specimen: length 93 mm.; height 100 mm.; diameter of both 

 valves 53 mm. 



Spondylus unicolor was described without indication of locality, but 

 there is little doubt that it represents the common form in the Gulf of 

 California. The subspecies differs from the typical form by its sparser sculp- 

 ture and wider primary interspaces, each bearing three smaller rows of 

 spines (secondary and tertiary). Many specimens show hardly any attach- 

 ment scars, and the two valves may be nearly alike in shape, convexity and 

 sculpture, and the colored inner band is often narrow. 



Range — Gulf of California and southward. Mexico: Gulf of California. 



Spondylus calclfer Carpenter Plate 22, figures 2, 2a 



Spondylus limbatus Reeve, 1856, Conch. Icon., vol. 6, Spondylus, pi. 9, fig. 54 Panama 



and Mazatlan. Not of Sowerby, 1847. 

 Spondylus radula Reeve, 1856, op. cit., pi. 14, fig. 52 Tehuantepec. 

 Spondylus calcifer Carpenter, 1856, Cat. Mazatlan Shell, Brit. Museum, pp. 152, 155 



Mazatlan. 

 spondylus smithi Fulton, 1915, Jour, of Conch., vol. 14, No. 12, p. 357, no. 66. New 



name for S. radula Reeve, not of Lamarck, 1806. 



Shell of medium or large size, often becomes coarse and heavy, rounded 

 or much deformed due to fixation and growth, the valves then unsymmetrical 

 in shape and in details of sculpture. Attachment is usually by a major part 

 of the surface of the lower valve, often along one side of the umbonal slope, 

 the free surface covered with foliated concentrics which aid in fixation. 

 Surface of the upper valve sculptured with numerous rows of radial spines, 

 short or of medium length; on the middle of the disk, these spines are 

 largest and of uniform size (not divided into sets of primary, secondary, 

 or tertiary strength) but diminish in strength towards the sides and may be 

 wholly absent from the anterior slope. Radial spaces between the ribs is 

 usually wide and plainly marked with fine and coarse threads, the middle 

 one sometimes bearing small spines. Color usually purple or violet, the 

 inner cavity white, the crural teeth brownish or more darkly stained, the 

 ventral margin bordered by a wide, deeply colored band. 



S. calcifer seems to be a distinct species although some shells may not 

 always be readily distinguishable from large, gerontic specimens of the 

 princeps group. A small shell figured by Myra Keen as the young of S. 

 calcifer is thickly covered with small thin spines and looks very different 

 from young shells of S. princeps of the same size. According to Carpenter, 

 Cuming first saw this species on a small island in the Bay of Panama, 

 where the natives dive for them to burn for lime. He broke up many speci- 

 mens for their contents, but they were to cumbrous for removal, "some of 

 them being more than a foot high and a foot broad". 



Range — Gulf of California south to Panama and perhaps to Peru. 

 Mexico: Mazatlan. Panama: Venado Beach; Pearl Islands. 



Family PLICATULTDAE 



Shell monomyarian, ostreiform, rounded, trigonal or spatulate, often 

 irregular but with the valves more or less equal in shape and sculpture, 

 solid, attached by the umbonal surface of either valve. Sculpture is formed 

 by coarse, radial ribs or sharp plications, sometimes smooth, the ribs irreg- 

 ular, wrinkled by lines of growth and in some species, coarsely scabrous 



