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851 



TERTIARY FAUNA OF FLORIDA 



beaks moderately elevated, small ; anterior end rounded, base prominently 

 arcuate ; posterior end pointed, hardly rostrate, with a single rostral carina, 

 below which the base is slightly emarginate ; sculpture of strong, rounded 

 undulations (about nine in number) not extending behind the carina, separated 

 by about equal interspaces ; sculpture feebler on the beaks ; rostral area con- 

 centrically striated ; lunular area slightly impressed but without any cellular 

 excavation ; surface, when perfect, with fine incremental lines and minute, 

 irregularly distributed radial threads; cardinal tooth strong; a small tubercle 

 on the hinge-margin of the left valve behind the chondrophore ; muscular 

 scars deep; pallial line with a small sinus. Lon. 15, alt. 10, diam. ^.6 mm. 



This species, though smaller, is externally very like the C. viminea, except 

 that the lunular area is only slightly depressed, so that if attention were not 

 particularly directed to it the depression might pass unnoticed, as it is not 

 definitely limited. 



Corbula (Bothrooorbula) radiatula n. s. 

 Plate 36, Figures 1-3. 



Upper Oligocene of Oak Grove, Santa Rosa County, Florida; Burns. 



Shell resembling the last species, but smaller, less high in proportion, and 

 longer, with the radiating threads more numerous and constant and the 

 lunular area more deeply impressed, forming an elongated cellule with definite 

 limits. Lon. 13, alt. 8.6, diam. 6.2 mm. 



Variety ienella Dall; shell quite thin and delicate, the surface closely 

 covered with minute radial threads. 



This species has the lunular depression intermediate in depth between 

 that of the last species and C. vuiiinea. 



To complete the account of this group, the following Pliocene species is 

 brought in here, somewhat out of its geological associations : 



Corbula (Bothrooorbula) Willcoxii n. s. 

 Plate 36, Figure 9. 



This species has the form of C. viminea, but is materially smaller ; it has 

 a deep hemispherical lunular depression unequally divided between the two 

 valves, much the larger part being excavated from the margin of the left 

 valve ; the surface is sculptured like that of C. synarmostes, the radial threads 

 being rather more numerous and the lunule quite different; in other respects 

 the hinge is similar to that of that species, and the general appearance of the 

 shell, except of the lunule, is much the same. Lon. 16, alt. 10, diam. 8 mm. 



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