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1173 



TERTIARY FAUNA OF FLORIDA 



Montacuta mariana n. sp. 

 PLATE 45, FIGURE 18. 



Miocene of St. Mary's River and Plum Point, Maryland ; Harris and the 

 State Geological Survey. 



Shell small, ovate, moderately convex, sculptured chiefly by incremental 

 lines and faint concentric wrinkles ; beaks conspicuous, showing the prodisso- 

 conch, but not high, nearly central ; the dorsal margin sloping almost equally 

 each way from the beaks, the ends rounded, the base evenly arcuate ; hinge 

 with a single small subtrigonal anterior lamina in each valve, a small oblique 

 submarginal sulcus in each valve behind the beaks ; interior of the valves 

 smooth, muscular impressions faint but normal. Lon. 4, alt. 3.25, diam. 1.5 

 mm. 



This species is smaller and more rounded than most of the Montacutas and 

 is apparently rather common in the St. Mary's Miocene. 



Montacuta petropolitana n. sp. 

 PLATE 45, FIGURE 6. 



Shell subtrigonal, rounded, moderately convex, inequilateral, the anterior 

 side longer; external surface nearly smooth with faint incremental lines and 

 a few minute sparsely distributed obscure granulations which may or may not 

 be a specific characteristic ; hinge with, in each valve, the anterior cardinal 

 tooth well developed, obliquely bent forward, and the anterior lamina absent, 

 as in the last species ; the posterior thickening over the resilium is small and 

 short, or more or less obsolete ; pit for the resilium elongated, narrow, and 

 distinct, hinge-plate flattish ; surface of the shell internally smooth or faintly 

 radially striated, the scars obscurely impressed. Lon. 5.75, alt. 4.5, diam. 2.3 

 mm. 



Two valves were obtained by Burns in the marl at Petersburg, Virginia. 



This species is puzzling and might easily be regarded as a Sportella, but 

 differs by having the slender cardinal bent back obliquely instead of projecting 

 in a straight line at right angles to the plane of the shell margin. It is also 

 less parallel-sided than most Sportellas, and the general aspect is more that of 

 Montacuta. From Sportella petropolitana, the most similar species known from 

 Petersburg, it is distinguishable at once by its less equilateral and more trigonal 

 shell, and the absence of the ligamentary nymphs. 



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