MARYLAND GEOLOGICAL SURVEY 721 



that they might be due in part to differences correlated with sex in this 

 genus.'' Dall, 1895. 1 



A. Posterior lateral margin obliquely truncate. 



1. Umbones anterior; anterior dorsal margin gently sloping. 



Panope decisa 



2. Umbones subcentral; anterior dorsal margin approximately 



straight Panope monmouthensis 



B. Posterior dorsal margin smoothly arcuate Panope bonaspes 



PANOPE DECISA Conrad 



Panopcea decisa Conrad, 1853, Jour. Acad. Nat. Sci., Phila., 2d ser., vol. ii, 



p. 275, pi. xxiv, fig. 19. 

 Panopcea decisa Meek, 1864, Check List Inv. Fossils N. A., Cret. and Jur., 



p. 15. 



Glycymeris decisa Conrad, 1868, Cook's Geol. of New Jersey, p. 727. 

 Panopea decisa Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 181, pi. 



xxiv, figs. 5-8. 



Panopea decisa Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 18. 

 Panopea decisa Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, p. 



646, pi. Ixxiii, figs. 3, 4. 



Description. " Oblong, ventricose, concentrically waved or furrowed ; 

 slightly contracted posteriorly; posterior hinge line nearly parallel with 

 the base; posterior margin truncated obliquely inwards; basal margin 

 nearly straight; beaks situated about one-third the shell's length from the 

 anterior margin." Conrad, 1853. 



TIJJJC Locality. ? Burlington County, New Jersey, or ? Chesapeake 

 and Delaware Canal, Delaware. 



" tShell moderately large and ventricose, with moderately large project- 

 ing beaks, which are situated a little nearer the anterior end. widely 

 gaping at the posterior end and closed anteriorly. Anterior extremity 

 rounded, longest below the middle, anterior end truncated, projecting near 

 the cardinal line and receding below. Surface of the shell marked by very 

 strong, broad, concentric undulations most strongly developed on the 

 middle of the valves and becoming nearly obsolete on some specimens 

 both anteriorly and posteriorly. The valves are also often depressed along 

 the posterior umbonal slope, showing a distinct furrow at the bending of 

 the undulations of the surface at this point. 



1 Trans. Wagner Free Inst. Sci., Phila., vol. iii, pt. iii, p. 827. 



