Maryland Geological Survey 511 



Class PELECYPODA 



order PRIONODESMACEA 



A. Taxodonta Neumayr (Emend) 

 Superfamily NUCULACEA 



Family NUCULIDAE Adams 



Genus NUCULA Lamarck 



[Prodr. Nouv. Class. Coq., vol. i, 1799, p. 87] 



T'ype. — Area nucleus Linne. 



Shell nacreous, small, trigonal to sub-circular or elliptical ; umbones 

 sub-central or posterior ; two series of transverse, numerous and close-set 

 hinge teeth, separated by a triangular chondrophore ; surface generally 

 smooth or concentrically striated ; margins simple or crenulate ; adductor 

 impressions sub-equal, two in number ; pallial line simple. 



A. Adult shell exceeding 15 mm. in latitude; true sculpture not developed. 



Nucula slackiana 



B. Adult shell not exceeding 15 mm. in latitude; concentric sculpture devel- 



oped from the umbones to the basal margin. 



1. Concentric sculpture comparatively coarse; radial sculpture devel- 



oped Nucula arnica 



2. Concentric sculpture microscopically fine Nucula microstriata 



Nucula slackiana Gabb 

 Plate XIX, Figs. 1-4 



Leda slackiana Gabb, 1860, Jour. Acad. Nat. Sci., Phila., 2d ser., vol. iv, 

 p. 397, pi. lxviii, fig. 37 (erroneously cited as 36). 



Nuculana slackiana Meek, 1864, Check List Invert. Fossils N. A., Cret. and 

 Jur., p. 8. 



Nucula slackiana Cook. 1868. Geol. New Jersey, p. 725. 



Nucula slackiana Gabb, 1876, Proc. Acad. Nat. Sci., Phila., p. 318. 



Nucula slackiana Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 103, 

 pi. xi, figs. 2, 3. 



Nucula slackiana Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 8. 



Nucula percrassa Weller, 1907, Geol. Survey of New Jersey., Pal., vol. iv, 

 p. 369, pi. xxix, figs. 1-5. (Synonymy and geographic distribution ex- 

 cluded.) 



Not Nucula percrassa Conrad, 1858. 



Description. — " Inequilateral (casts) : muscular scars large and deep; 

 margin crenate; cardinal line apparently curved, basal irregularly 



Etymology. Nucula. a little nut. 



