32 BuivLKTiN 31 33 



Type and specimen figured. — Paleont. Mus. Cornell Univ. 



Horizon. — St. Maurice Stage. 



Locality. — Columbus road, 5 miles N. of Orangeburg, S. C. 



Modiolus (Mauricia) houstonius Harris, PI. 17. Fig. 5-a, 



Modiola hotistoiiia Har., Proc. Phila. Acad. Nat. Sci., 1895, p. 46. pi- 



I, fig. I. 

 Lithophaga houstonia Dall, Trans. Wag. , III, '98, pp. 798, 8or. 



Mauricia, n. sub. gen. 



Spathella-shape, with undulations on post-umbonal slope, 

 dying away on area below the ridge ; fine radii upon and above 

 the ridge ; Brachidontes radii on the anterior ; .shell thin, per- 

 laceous. 



Harris's original description of houstonia. — General form of shell as 

 figured ; thin, showing concentric lines of growth on the area below the um- 

 bonal ridge ; above the same with broad, concentric undulations, becoming 

 more numerous towards the umbones ; anterior radially striate. 



We cannot accept Ball's reference of this peculiar form to 

 Lithophaga becaue of : ist, the well defined umbonal ridge ; 2d, 

 the radiating lines mediallj^, and the stronger ones on the anter- 

 ior, and 3d, the total lack of the encircling or zonal sculpturing 

 so common in Lithophagcs and evidentl}^ a result of rotary motion 

 in their excavations. 



Type and specimens figured. — Texas Univ. Coll. Mus. No. 



145- 



Horizon. — St. Maurice Eocene. 



Localities.— lihr^Q miles N. E. of Crockett, Houston Co., 

 Texas ; Chautauqua, I^a. ; 5 miles N. W. of Orangeburg S. C. 



rt^odioius texanus Gabb, PI. 17. Figs. 6, 7 



Perna texana Gabb, Proc. Phila. Acad., 1861, p. 371. 



Modiola texana Har., Proc, Phila. Acad., 1895, p. 46, pi. i, fig. 2. 



Gabb^s original description. — Elongated, subtriangular. Bealc^ term- 

 inal, small ; umbones prominent, though small ; anterior end rounded, nar- 

 row ; cardinal margin straight, basal broadly sinuous ; posterior basal angle 

 abruptly rounded ; posterior edge broadly convex, uniting with a regular 

 curve with the cardinal line. Umbonal ridge high, convex ; anterior slope 

 abrupt and slightly convex near the margin towards the beak, between 

 which convexity and the ridge is a slight concavity ; posterior slope regular. 



