9-3 St. Maurice and CLx\iborne Pelecypoda 95 



figure. The difference in length of the anterior and posterior 

 sides is much greater than in parvus, its nearest relative. Again 

 the basal margin is remarkabl}^ rounding. 

 Micromeris minutissima Lea, PI. 32. Figs. 24, 25. 



Astarte minutissima Lea, Cont. to Geol., 1833, p. 64, pi. 2, fig. 39. 



Micromeris minutissima Con., Smithson Misc. Coll., 1866, p. 5. 



f Micromeris senex Meyer, Bull, i, Geol. Surv. Ala., 1886, p. 81, pi. 3, 



fig. 22. 

 Crassatellites {Micromeris) mifiutissima Dall, Trans. Wag., Ill, 1903, 



p. 1480. 



Lea's original description. — Shell scaleniform, acutely angular 

 above, rather compressed, oblique, ribbed longitudinally ; beaks elevated, 

 pointed ; lunule very large, cordate ; cardinal teeth small, the posterior 

 margin furnished w^ith a long straight lateral one ; cicatrices scarcely visi- 

 ble ; margin largely crenate. 



Diam Length i -20th, Breadth i-20th of an inch. 



Type. — Phila. Acad. Nat. Sci., No. 5231. Regarding this type I find 

 in my notes : "Evidently the type of the right valve figured, though the 

 small figure given is too large and the large figure has too many ribs. This 

 has but twelve". 



The specimen in our collection figured herewith (pi. 33, figs. 

 24-25) is also comparatively few ribbed, likewise Meyer's senex, 

 referred to above. Meyer gives a very poor figure of his speci- 

 man and describes it as follows: "Shell solid, anterior margin 

 straight, posterior margin curved ; surface, except the umbo, 

 covered with coarse, radiating ribs" . Claiborne bed "G". How- 

 ever this would appear to be from a basal Jackson bed. 



Pleuromeris aldrichi, n. sp., PI. 32. Figs. 26-29. 



Specific characterization. — Shell very minute and rather ro- 

 tund as indicated by the figures ; substance of the shell not thick, 

 smooth and glossy within ; exteriorly showing 1 1 or 1 2 verj^ well 

 defined strong ribs except on the apical region where there are 

 rather well defined concentric markings ; posterior, subligamen- 

 tal margin, as in some sections of the Veneridtz with well-raised 

 flanges cutting across the concentric lines at an oblique angle ; 

 interiorly, showing position of ribs and very faint muscular scars ; 

 lunule and escutcheon both somewhat pouting not far below the 

 apex ; ligament scarcely showing above the margins of the shell ; 



