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1470 



TERTIARY FAUNA OF FLORIDA * 



cavated than the former and wider ; both are smooth ; base arcuate ; disk 

 sculptured with rather close-set, regular, subequal, flattish, concentric ridges 

 with narrower interspaces ; these are sometimes feebly elevated, but preserve 

 their general close-set, regular character ; hinge well developed, the posterior 

 cardinal in the left valve often conspicuous. Height 3.2, breadth 3.2, diameter 

 1.7 mm. 



This species is especially characterized by the closeness, regularity, and 

 smoothness of its concentric ridges and the long and narrow lunule and 

 escutcheon. 



Crassatellites (Crassinella) acutus n. sp. 

 PLATE 50, FIGURES i, 4. 



Pliocene of the Caloosahatchie, Shell Creek, and Alligator Creek, Florida ; 

 Willcox, Burns, and Dall. 



Shell small, solid, with very acute, slightly backwardly deflected beaks and 

 wide, compressed base ; lunule and anterior slope straight, of equal length, 

 the lunule moderately impressed and smooth ; posterior slope longer, somewhat 

 excavated, the escutcheon well impressed, and in specimens with strong sculp- 

 ture the carina bounding the escutcheon is often crenulated by the ends of the 

 concentric ribs ; sculpture of (about fifteen) medially rather elevated, narrow, 

 even, regular, rounded ribs with much wider excavated interspaces, the ribs 

 less conspicuous near the base and varying somewhat in strength in different 

 individuals ; disk but slightly convex, compressed towards the base, so that a 

 section in profile would be wedge-shaped ; hinge strong, the posterior cardinal 

 in the left valve prominent but more or less coalescent with the dorsal margin. 

 Height 4.0, breadth 4.3, diameter 1.8 mm. 



This is a well-marked and pretty uniform species quite abundant in the 

 Caloosahatchie Pliocene. The recent forms of the Atlantic coast may all be 

 referred to the C. lunulatus Conrad, though t the varieties are numerous. The 

 Pacific C. pacificus is hardly distinguishable from C. lunulatus, but the C. 

 varians Carpenter is a very well-defined form, characterized by its Meretrix- 

 like outline, which is quite different from any of the other species. It ranges 

 from Cape St. Lucas to Mazatlan, while C. pacificus has been obtained from 

 San Diego, California, south to Panama. 



Subgenus MICROMERIS Conrad. 



Astarte (sp.) Lea, Contr. Geol., p. 64, 1833; H. C. Lea, Cat. Tert. Test, of U. S., p. 4, 

 1848. 



