Bkede.] Carboniferous Invertebrates, 13o 



a little more convex, having regular striae, and in being a little 

 smaller. P. cf. hawni, in the article above referred to, should also 

 be considered as a true member of the species. The species here 

 separated are, 1 believe, distinct from P. Juuviii ; and this variety 

 is worthy of varietal distinction, as often shells of these kinds are 

 found in localities where the others are absent and some method 

 of distinguishing the two forms of the species is necessary. 



POSIDONOMYA. 



Bronn. Letb. Geogn., (1837). 



Posidonomya? recurva. Plate XIX, figs. 6-6c. 



Posidonomya f recurva Beede, Kans. Univ. Quart., vin, p. 126, pi. xxxn, 

 f. 6, (1899). 



Shell of medium size, lenticular, oblique, and thin. The hinge 

 line is nearly straight, about two-thirds the length of the shell. 

 The beak is moderately prominent, recurved, projecting very 

 slightly beyond the hinge. The greatest convexity is on the 

 upper half of the shell and constitutes the umbonal swell, which 

 is moderately prominent and curved backward, making the 

 shell oblique. The surface is marked by concentric undula- 

 tions of growth, and fine, closely set, concentric striae. Height, 

 23 mm. ; length, 23 mm. ; convexity of valve, about 4 mm. 



Range and distribution : Upper Coal Measures ; Lawrence. 



A specimen from the dam, at Lawrence, and shown in figs. 

 6b, 6c, Plate XIX, is probably of the same species, though it has 

 a somewhat different appearance and outline. It shows the 

 beak projecting beyond the hinge, and the cast of the interior 

 shows the beak to have been hollow beyond the hinge. The 

 cast figured is of both valves in place, one of which is slightly 

 crushed. It may be a distinct species, though as it is from the 

 same horizon it is probable that the difference is individual 

 rather than specific. 



The character of the hinge and the internal markings are too 

 poorly shown in our specimens to permit of accurate location 

 of the species. It resembles very much in appearance species of 

 the genus Posidonomya, to which it is provisionally referred, and 

 with which it agrees in its surface markings and in having a 



