142 BULI.ETIN 31 143 



borne. One valve is in the U. S. Nat. Museum. The type and 

 the one herewith figured are at Cornell. 



In the Jackson stage seairiformis typically is decidedly dis- 

 tinct from nuttali, but many are the forms of this species at 

 Montgomery, La., scarcely distinguishable from varieties of /^x- 

 acola and nuttalliopsis. 



Aequorea is by far the most abundant at Claiborne. It 

 may be distantly related to the perovata stock. Percrassa, though 

 thick umbonally, probably belongs with trigoniata. 



Meretrix texacoia Harris, PI. 44, Figs. 13-15. 



PI. 45, Figs. 1-3. 

 M. texacoia Har., Proc. Phila. Acad. Nat. Sci., 1895, p. 50, pi. 2, fig. 5 



Harris'' s original description. — Size and general form as indicated by 

 the figures ; surface generally smooth about the umbones, but often more 

 or less corrugated concentrically towards the base, especially posteriorly ; 

 lunule in the larger specimens very indistinct, in the smaller forms bor- 

 dered by a well incised line. 



The surface markings somewhat resemble those of C. nuttalliopsis 

 Heilp. , but the anterior and posterior are too pointed, the shell in general 

 too inflated, and the umbonal angle too great for that species. The larger 

 specimens resemble M. californica Con. 



Occasional specimens of medium size, referable to this spe- 

 cies, seem to practically connect such nearly related forms as 

 nuttalliopsis, nuttali, and varieties of securiformis ; hence, in a 

 sense, most of these designations might be regarded as varietal. 

 In Texas, we formerly designated the smaller, longer forms (pi. 

 45, figs. 2, 3), as var. tornadonis. Another Texan form simu- 

 lating in type of exterior marking the mortoni of Conrad is 

 shown by fig. I . It seems however to be simply a sport from 

 the texacoia stock. 



Type. — Texas Museum. 



Horizon. — St. Maurice Eocene. 



Specimens figured. — PI. 44, figs. 13, 14, Tex. Mus, Fig. 12, 

 lyisbon, Ala., C. U. Pal. Mus. PI. 45, figs. 1-3, Texas State 

 Mus. 



Localities. — Texas : Rio Grande at Webb-Zapata county 

 line ; Smithville, Bastrop Co. ; 2 miles E, of Alto, Cherokee ; 



