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895 



TERTIARY FAUNA OF FLORIDA 



Shell small, solid, inequilateral, subovate, externally marked by lines of 

 growth and fine, slightly oblique, irregular wrinkles ; the fossil shows distinct 

 traces of radial bands of color; anterior end shorter, rounded, the dorsal area 

 faintly impressed ; posterior end longer, somewhat recurved, the dorsal area 

 narrow, excavated, elongated, bordered by a broad, impressed fasciole bounded 

 on each side by an elevated line, and extending backward from the umbo ; 

 base of the shell markedly arcuate; valves rather convex; the pallial sinus 

 broad, rounded, not reaching the middle of the valve ; hinge normal, the 

 ventral border of the chondrophore projecting, the teeth short and strong; 

 the dentate appearance caused by the fusion of the anterior arm of the car- 

 dinal teeth with the ventral lamina is very marked. Lon. 44.5, alt. 30, diam. 

 17 mm. The posterior end has a pronounced gape. 



A single specimen of this well-marked species was found among the 

 fossils presented by Mr. Willcox to the National Museum. It is heavier, 

 more inequilateral, and more arcuate than specimens of M. fragilis of the 

 same length. 



Subgenus MACTRELLA Gray. 



Mactra (Mactrella ?) darienensis n. s. 



Shell small, short, inflated, trigonal, thin, with very high and prominent 

 beaks ; surface smooth or minutely undulated, angulated posteriorly by the 

 line bounding the dorsal area ; anterior dorsal area impressed, with the dorsal 

 shell margin reflected upward : both the anterior and posterior areas are 

 broad, and distinctly, regularly, sharply, concentrically grooved; posterior end 

 shorter than the anterior, obtusely angular below; anterior end produced 

 and rounded, depressed above. Lon. 22, alt. 18, semidiam. 5.5 mm. 



This species is represented by a right valve, partially lost from the cast, 

 in a grayish marly rock, which does not disclose the hinge, and therefore 

 it cannot be positively stated to be a B'lactrclla, but the form of the shell and 

 all the attendant circumstances leave little doubt in my mind that it is cor- 

 rectly placed in that group. 



It is found with Turritclla gatunensis, Cytlierea dariena Conr., and Glyp- 



iostyla panainensis Dall, in the Eocene Gatun beds, corresponding to the 



Claibornian, at Vamos-vamos Station on the line of the Panama Canal, Isthmus 



of Darien. 



Geuus SPISULA Gray. 



Spisula Gray, Mag. Nat. Hist., i., N. S., p. 372, 1S38. 



Spissula Phil, non Morch ; Spi:^tila pars Morch, and Spisuliiia Fischer, 1887. 



