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597 



TERTIARY FAUNA OF FLORIDA ^^ ' 



distinguished by the less arcuate base, more attenuated anterior end, some- 

 what more compressed form, and, in the great majority of specimens, by 

 having on the convexity of the beaks and the early part of their posterior 

 slope a concentric sculpture of fine even riblets with about equal interspaces. 

 There is also on the escutcheon an elevated radial line, absent on the corre- 

 sponding part of Y. Icevis, which also attains a nearly one-third larger size 

 when full grown. There are about twenty-six teeth on each side of a small 

 subumbonal chondrophore. Lon. 19, alt. 8, diam. 4 mm. 



This shell is perhaps the ancestor of Y. Icevis, from which it can usually 

 be readily distinguished by its more rectangular form and sculptured umbones. 



Yoldia tarpseia n. s. 



Chesapeake Miocene of the upper bed at Alum Bluff, Calhoun County, 

 Florida; Dall and Burns. 



Shell small, smooth, ovoid, moderately convex, rather solid for its size, 

 with the ends rounded, the posterior smaller, the base evenly arcuated ; lunule 

 very narrow ; escutcheon smooth, or marked only by lines of growth, with a 

 single lamellose elevated line very close to the shell margin, which in young 

 or worn specimens is often obscured; beaks low, hinge-line nearly straight, 

 pallial sinus rounded, deep, nearly reaching the vertical of the beaks ; about 

 twenty anterior and eighteen posterior small, narrow teeth, separated by a sub- 

 umbonal chondrophore. Lon. of a large specimen, 14.25 ; a perfect but smaller 

 one measures, lon. 9.5, alt. 5, diam. 3 mm. 



This shell recalls Y. sapotilla Gld., and bears to Y. lavis much such a 

 relation as Y. sapotilla does to Y. limahila Say. 



Subfamily MALLETIIN/E. 

 Geuus PLEURODON S. Wood. 



PletirodonW oodi, Charlesworth's Mag., iv., p. 230, 1840. (Type P. ova/isWood, op. cit., p. 



230, suppl. pi. xiii., fig. I a-d.) Not Pleurodonte Fischer, Tab. Syn. Zoog., p. 129, 1808. 

 Nuculifia Orbigny, Pal. Franc, iii., p. 161, 1843. (Type Nuctila miliaris Deshayes, non 



Wood, Coq. env. Paris, i., p. 235, pi. x.xxvi., figs. 7-9, 1824.) Not Nuculina Agassiz 



or Filippi. 

 Niicinella Wood, Crag. Moll., ii., p. 72, 1850. i^N. miliaris Wood, non Deshayes, pi. x., 



figs. 4 a-c, 1850.) Deshayes, An. s. Vert, bassin de Paris, i., p. 826, i860. 

 Nuculina E. A. Smith, Challenger Pelecypods, p. 230, 1885. Verrill, Am. Journ. Sci., 



Jan., 1897, p. 51. 



