208 SYSTEMATIC PALEONTOLOGY 



coast and differs from the northern forms and those found in the fossil 

 state. Th,e latter, he says " are almost smoothly truncate behind, the es- 

 cutcheon is not impressed to any marked degree, and there is no angle 

 at the margin below the escutcheon.''* To these forms he has given the 

 varietal name of trunculus. He thinks that the fossil forms correspond 

 to the cooler temperature of the sea in geological time. 



The earliest appearance of this species is in the Miocene of New Jer- 

 sey, Maryland, and Virginia. It is found in the Pliocene of South 

 Carolina and Florida, and in the Pleistocene of Mar}dand and South 

 Carolina. In the Eecent it ranges from Nova Scotia to Florida. 



Width, 4.5 mm.; height, 4 mm. 



Occurrence. — Talbot Formation. Wailes Bluff near Cornfield Har- 

 bor, St. Mary's County. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 and U. S. National Museum. 



Genus LEDA Schumacher. 



Leda acuta (Conrad). 



Plate LXV, Figs. 5-8. 



Nucula acuta Conrad, 1832, Amer. Mar. Conch., p. 32, pi. vi, fig. 1. 

 Nucula acuta Conrad, 1845, Fossils Medial Tertiary, p. 57, pi. xxx, fig. 2. 

 Nucula acuta Holmes, 1858, Post-PL Fos. S. C, p. 16, pi. iii, fig. 7. 

 Leda acuta Dall, 1889, Bull. U. S. Nat. Mus., No. 37, p. 44, pi. vii, figs. 3 and 



8; pi. xlv, fig. 15; pi. lxiv, fig. 140. 

 Leda acuta Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, pt. 4, pp. 



592, 593. 



Description. — " Ovate-lanceolate, ventricose, with prominent concen- 

 tric striee; anterior side longest, rostrated, compressed, acute at the ex- 

 tremity, which is lightly recurved; anterior submargin carinated; pos- 

 terior end acutely rounded; basal margin profoundly curved, slightly 

 sinuous near the anterior extremity, obliquely subtruncated towards the 

 posterior extremity." Conrad, 1845. 



This very widely distributed species shows much variation in external 

 sculpture, the strise at times partly disappearing and at otlicr times 1m-- 



