HEEDE: NEW FORMS OF PSEUDOMONO ll S. 8l 



seem to form a distinct group by themselves, and the second may, 

 possibly, prove to be a variety of the first, though our material 

 does not indicate that such is the case. 



PseudomoiiDiis (?) tenuistriata sp. ('') var. ('^) nov. 



Shell large, ovate in outline, rather compressed, beak moderately 

 prominent, projecting beyond the hinge which is nearly straight. 

 Anterior ear small, rounded to meet the hinge, rather flat, the shell 

 rising rather abruptly to the swell of the umbo; anterior margin 

 slightly sinuate, antero-ventral margin very broadly rounded to the 

 ventral portion of the shell where it becomes nearly straight, then 

 rounding more abruptly to the posterior ear, which is also rounded 

 to the hinge. Greatest convexity a trifle below the beak, but is 

 very slight there. The surface is marked by many fine, wavy, 

 radiating striae of uniform size extending from the beak to the 

 ventral margin; occasionally one striation will be a trifle larger 

 than the other on the central part of the shell, but it soon loses 

 itself, and on old individuals the stria^ on the ventral border are all 

 about uniform. They increase by interpolation and are rather 

 sharply defined, separated b}^ troughs from one to three times their 

 width, and are generally crossed b}^ fine concentric lines or laminae. 

 Right valve unknown. Measurements: height 62 mm., length 

 60 mm.,* convexity 10 mm., length of hinge 23 mm. 



Upper Coal Measures; Turner, Wyandotte county, Kansas. 

 Also Topeka; Auburn, Shawnee county, Kansas. 



In some respects this shell seems to be related to P. i:;iganteus 

 Waagen, from the salt range of India, but differs in being com- 

 paratively higher and shorter, and in having much more regular 

 surface markings and less developed ears. It seems well removed 

 from P. Itatvni and spcliuiiaria and their varieties. 



There seems to be another form of this species or variety, having 

 a much longer hinge, and with the adult much more convex, while 

 the surface is more roughly marked, and the striae more variable. 

 Two 3^oung individuals of these shells are figured in Plate XVTII, 

 figs, ic and id, showing the great length of the hinge and the 

 variation in the ears 'in the young of that form. The young are 

 not very convex but the older ones are much more convex as a 

 rule, as is shown in figure ib of the plate referred to. The striae 

 differ much more in size in the old than in the young individuals, 

 and I am inclined to think that it will prove varietally distinct 



♦The specimen us«d as tlie type is somewhat crushed on the posterior end. making 

 the shell appear longer ihnn it really was. The length given here is that of the 

 specimen in its crushed condition. 



