^l PROCEEDIlSrGS OF THE NATION^^X, MUSEUM. vol. 61. 



cardinals and laterals, some have pseudocardinals only, and others 

 have neither. 



Genotype.— Diplodontites cookei, new species. 



DIPLODONTITES COOKEI. new species. 



Plate 1, figs. 1. ?,, 7, 8, 10; plate 3, fig. 4. 



Shell moderately thick, elliptical in outline, rounded anteriorly and 

 posteriorly. Slightly gaping in front, posterior dorsal margin lightly 

 arched, the dorsal ridge rather full and rounded, beaks moderately 

 elevated (so eroded that any sculpture that may have existed is lost). 

 Periostracum clothlike, dull, closely adhering, showing no tendency 

 to j)eel. Color yellowish olive, the posterior dorsal area of each valve 

 with 10 radiating greenish stripes, Eadiating sculpture consisting 

 of a number of clearly defined impressed lines which are nearly 

 equally spaced and between wdiich are many microscopic radiating 

 slightly waving, striae — about 40 of these striae between each pair 

 of impressed lines. With sufficient magnification each of these striae 

 is seen to consist of innumerable granules. Concentric sculpture con- 

 sisting of many irregular, slightly raised minor lines of growth, which 

 are interrupted by each of the radiating impressed lines, between 

 each pair of which the concentric lines bend downward in directions 

 radiating from the beaks, crinkling and drooping like festooned drap- 

 ery. To the naked eye this festooning is hardly visible, but under a 

 lens it becomes one of the most striking features. Three principal 

 stages of growth are indicated. Color of interior varying from whit- 

 ish to pinkish, moderately iridescent, anterior adductor scar impressed, 

 deep at its upper end, posterior scar but lightly impressed. Sinulus 

 triangular like that of Anodontites. No lateral teeth in either valve. 

 Right valve with three pseudocardinal teeth, the front one being 

 strongest, high and triangular, the second low and longer, the pos- 

 terior one indistinctl}^ differentiated from the hinge plate. The 

 socket between the first and second is large, deep, triangular, the socket 

 between the second and third is a lengthened narrow groove, its bot- 

 tom and walls with many sharp defined lines of growth. Left valve 

 also with three pseudocardinal teeth, the front one nearly obsolete, 

 the middle one being very large and triangular, the posterior one long 

 and low. The socket between the first and second is verj' deep, that 

 between the second and third is similar to the corresponding socket 

 in the right valve and has similar growth markings. Prismatic bor- 

 der narrow, greenish-olive, minutely granulous. 



The type (Cat. No. 341473, U.S.N.M.), measures: Length 53 mm., 

 height 32 mm., diameter 20 mm. It and two other specimens and an 

 odd valve come from a tributary of the Eio Colorado (which in turn 

 becomes tributary to the Rio Magdalena), in the Province of San- 



