INVKUTKHKATK PALEONTOLOGY. 12 l J 



Devonian, or possibly even the Silurian, period, and ranged through all sub- 

 sequent epochs to the present time. The species, however, seem never to 

 have been very numerous. At present, only some tour or five recent species 

 are known. Of these there occur two on the eastern coast of the United 

 States, while the others are from New Zealand, New Holland, the Mediter- 

 ranean, West Africa, &c. They are found burrowing in muddy bottoms 

 at a depth of about two fathoms. 



Sole in y a subplicata, M. &H. 



Plate 28, fig. 19. 



SoUm subplicata, Meek and Haydeu (1856), Proceed. Acad. Nat, Sci. Philad., VIII, 82. 

 Solemya subplicata, Meek (1864), Smithsonian Cueck-List N. Am. Cret. Fossils, 11. 



Shell nearly three times as long as high, moderately compressed, 

 extremity thin and fragile; cardinal and basal margins straight and parallel; 

 anal extremity obliquely rounding to the base; anterior end rounding up from 

 below, and apparently obliquely declining above; beaks near the posterior end, 

 not distinct from, nor rising above, the dorsal border. Surface ornamented 

 by very fine, obscure stria?, of growth, crossed on the anterior side by broad, 

 nearly obsolete, radiating costse, some six or eight of which extend to the anal 

 margin, to which they seem to impart a very slightly-waved outline. 



Length, about 1.10 inches; height, 0.42 inch; convexity, 0.26 inch. 



The radiating plications are very obscure, and might be overlooked. 

 They are most distinct on the antero-dorsal region, and gradually fade away 

 on the middle and posterior portions of the shell. In some cases, by the aid 

 of a good lens, in a favorable light, traces of very minute, closely-set stria? may 

 be seen crossing the lines of growth. These do not appear to radiate from 

 the beaks, but to cross the surface at right angles to the longer diameter of 

 the shell, and are quite as distinct on the inside as on the outside. These 

 may, however, be due to the shell-structure rather than to surface-markings. 



On casts, two shallow depressions are" seen near the posterior side of the 

 beak of each valve, one extending obliquely forward close to the truncated 

 posterior border, and the other a little farther back, passing less obliquely 

 downward. They seem to have been occupied by callosities connected with 

 the hinge on the interior of the valves. 



Locality and position. — Moreau River; in the Fox Hills group, or forma- 

 tion of the Upper Missouri Cretaceous series. It is very rare; only a 

 single specimen being yet known. 

 17 H 



