554 Systematic Paleontology 



Ostrea laeva var. nasuta Morton 

 Plate XXII, Fig. 5 



Ostrea falcata var. A (0. nasuta), Morton, 1834, Syn. Org. Rem. Cret. Group, 



U. S., p. 51, pi. ix, fig. 6. 

 Ostrea ungulata (Schlotheim) Coquand, 1869, Mon. Genre Ostrea, p. 58, pi. 



xxxi, figs. 6-9 (ex parte). 

 Ostrea (Alectryonia) larva White, 1884, 4th Ann. Rep. XJ. S. Geol. Survey, 



p. 296, pi. xlii, figs. 2-5, 9 (ex parte). 

 Ostrea larva var. nasuta Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, 



p. 34, pi. iii, figs. 3, 4 (ex parte). 

 Ostrea larva Hill, 1901, 21st Ann. Rep. IT. S. Geol. Survey, pt. vii, pi. xlviii, 



fig. 66a. 

 Ostrea larva Hill and Vaughan, 1902, XJ. S. Geol. Survey, Geol. Atlas, Austin 



Folio, fig. 50. 

 Ostrea larva Veateh, 1906, Prof. Paper U. S. Geol. Survey, No. 46, pi. xi, figs. 



1, la, 7. 

 Ostrea nasuta Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, p. 447, 



pi. xliii, figs. 7, 8. 



Description. — " Smooth, expanded, compressed ; with three or four 

 strong marginal plications." — Morton, 1834. 



Type Locality. — ? St Georges, Delaware. 



Shell rather large for the group, thin, very brittle, compressed, later- 

 ally expanded and feebly arcuate ; quite strongly auriculate, as a rule, the 

 posterior auricle often larger than the anterior which is occasionally 

 reduced or even atrophied ; left valve only moderately convex, right valve 

 flattened, both valves radially plicate marginally and sculptured with fine 

 but obvious incrementals, plications broadly undulatory on the convex 

 margin, three to seven or eight in number, reduced to marginal crenula- 

 tions on the inner concave surface. Medial portion of the shell unaffected 

 by the radials. Hinge line straight, ligament area small, trigonal, 

 usually medial, groove shallow ; muscle scar semi-elliptical, a little behind 

 the median horizontal. Inner surface plicated in harmony with the 

 external sculpture. 



O. larva var. nasuta runs the longest of any of the larva group except- 

 ing falcata. It is best characterized by the very broad, only moderately 

 deep undulations of the convex lateral margins. O. larva var. mesen- 

 terica is a smaller form, more strongly arcuate, less conspicuously auricu- 



