MARYLAND GEOLOGICAL SURVEY 583 



Trigonia eufalcnsis Conrad, 1868, Cook's Geol. of New Jersey, p. 725. 

 Trigonia eufalensis Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 113, 



pi. xiv, figs. 1-4. 



Trigonia eufalensis Johnson, 1905, Proc. Acad. Nat. Sci., Fhila., p. 11. 

 Trigonia eufalensis Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, 



p. 462, pi. xlviii, figs. 5-10. 



Description. " Subtriangular, resembles T. alceformis Sow. in out- 

 line, not quite so elongate anteriorly; beaks posterior; lunule distinct; 

 surface marked by about fourteen ribs, the more anterior of which pro- 

 ceed from the lunule anteriorly and then cross the shell at right angles 

 with the lunule, exhibiting a tendency to being nodose, especially near 

 the lunule; lunule marked by ten or twelve transverse ribs; cardinal 

 margin somewhat incurved, anterior elongate and subbiangular, basal 

 sinuous and deeply serrate, posterior regularly rounded ; internally, hinge 

 teeth small, muscular impressions deep ; pallial line entire ; a small tooth- 

 like ridge or process extends along the middle of the alation, as in 

 T. alceformis." Conrad, 1860. 



Type Locality. Eufaula, Alabama. 



Shell thick, heavy, prismatic, rudely trigonal in outline, moderately 

 convex ; umbones anterior, incurved, opisthodetic, flattened upon their 

 summits but prominent by reason of their position at the apex of an angle 

 of approximately 120 ; lunule not differentiated, escutcheon denned, not 

 only by the sculpture but also by an abrupt change in the plane of the 

 shell ; anterior portion of the shell sculptured by twelve to fifteen promi- 

 nent concentric ridges, rather sharply rounded upon 'their summits, dor- 

 sally inclined, especially in the umbonal region, more prominent, sym- 

 metrical and feebly rugose ventrally, regularly arranged but much more 

 closely spaced along the concave margin than the convex ; ligament mar- 

 ginal the groove in which it was lodged short linear and opisthodetic; 

 cardinal teeth of left valve massive, trigonal, transversely striated, inner 

 faces of hinge margins also striated in order to clasp the divergent teeth of 

 the right valve ; muscle impressions deeply excavated, the anterior slightly 

 more so than the posterior; pallial line simple distant from the hinge 

 margin. 



