95 St. Mauricp: and Claiborne 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 remarkably rounding. 



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



Astarte minutissima Lea, Cont. to GeoL, 1833, p. 64, pL 2, fig. 39. 



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



? Micromeris senex Meyer, BulL i, GeoL Surv. Ala., 1886, p. 81, pL 3, 



fig. 22. 

 Crassatellites {Micromeris) iiiiuutissiiiia Dall, Trans. Wag., IIL 1903, 



p. 1480. 



Lea's original description. — Shell scaleniform, acntel}'- angular 

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

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

 margin furnished with a long straight lateral one ; cicatrices scarcely visi- 

 ble ; margin largely crenate. 



Diam Length i-2oth. Breadth i-2()th of an inch. 



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

 in my notes : "F.vidently 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 Mej^er's se^iex, 

 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., PL 32. Figs. 26-29. 



Specific characterizatio7i. — Shell very minute and rather ro- 

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

 smooth and glossy within ; exteriorly showing 11 or 1 2 very 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 Veneridce with well-raised 

 flanges cutting across the concentric lines at an oblique angle ; 

 interiorly, showing position of ribs and verj^ faint muscular scars ; 

 lunule and escutcheon both somewhat pouting not far below the 

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



