148 Bulletin 31 148 



matrix, derived evidently from weathering of glanconitic, sand}^ 

 clays. The exact locality in Winn Parish, Ivouisiana, from 

 which the material was obtained is not given but it appears to be 

 exactly the same as we have collected along the St. Maurice road 

 leading past the "Marble Quarry" west of Winnfield. Speci- 

 mens deposited by Harris in the Pal. Museum, Cornell Univer- 

 sity. 



Meretrix trigoniata var. bastropensis, nov. var., PI. 47, Figs. 4-6 



Cytherea nuttali Con., U. S. & Mex. Bound. Sur\'., Geol. and Paleont- 



1857, p. 162, pi. 4, fig. 5. 

 ? Caryatis exigua Con., Amer. Jr. Conch., vol, 6, 1871, p. 201, pi. 11, 



fig- 3- 

 Cytherea discoidalis Heilp, , Proc. Acad. Nat. Sci., Phila. , 1890, 



p. 402. 

 Cytherea tiuttattii Heilp., ibid. 

 ? Mysia ungulina Heilp., ibid. 



Specific characterization. — General form as figured : possess- 

 ing two aspects according to the kind of matrix in which it is 

 preserved: ist, when preserved in clay or ferruginous sand. — 

 Substance of shell thin ; small ; external surface with beautiful, 

 evenly sculptured concentric strise ; lunule large, long, defined 

 by a very faintl}^ impressed line ; somewhat resembling trigon- 

 iata Lea, though too circular in outline (fig. 4). 2d, when pre- 

 served in firm calcareous sandstone. — Shell comparatively larger, 

 thicker, with less plainly marked concentric strise on the um- 

 bones and much coarser lines or rugae near the anterior, basal 

 and posterior margins (fig. 6). This form is very similar to 

 that described by Conrad as Dosinia alta, from Canj^ada de las 

 Uvas, California. The figure he gives is exceedingly^ poor and 

 misleading. The type specimen, or that marked as such and 

 broken in the manner illustrated, is in the collection of the U. S. 

 National Museum. 



This species is generally characterized by the broad, circular 

 form of its posterior margin. The form together with the char- 

 acter of the concentric strise or rugse on the larger specimens 

 found along the Rio Grande will serve to differentiate it from 

 trigoniata or nuttali. In the last mentioned species the ru- 



