692 SYSTEMATIC PALEONTOLOGY 



always have a short ligament. The resilium is usually enclosed in the 

 hemicylindric ligament. In some forms, however, as Metis and Tellidora, 

 the resilium is much shorter than the ligament and evinces a tendency to 

 become internal as in the Semelidce. The exterior sculpture of the Tel- 

 Unas is emphatically concentric, though fine radial sculpture often exists, 

 it does not, except in the section Pseudarcopagia, rival the concentric 

 sculpture in strength. There is no known species with only radial sculp- 

 ture. Oblique or angular sculpture is rare. The posterior end of the shell 

 is usually flexed to the right and exhibits one or more folds of greater or 

 less prominence. Occasional marked inequality of the valves is observable, 

 and the culmination of the surface ssculpture as it passes over the ridges 

 which radiate from the beaks toward the end of the valves sometimes 

 results in elegant lamelliform prominence." Dall, 1900. 1 



The genus was initiated in the Jurassic and has been abundantly repre- 

 sented since the late Mesozoic. The recent species are numbered by the 

 hundreds and are particularly characteristic of the tropical and sub- 

 tropical seas. 



A. Altitude of shell approximately one-half the latitude. . . .Tellina georgiana 



B. Altitude of shell more than one-half the latitude Tellina gabbi 



Subgenus ARCOPAGIA Brown 

 [111. Conch. Great Britain, 1827, p. ii, pi. xvi, fig. 8] 



"Shell large, solid, rounded, moderately convex, the flexure obsolete; 

 posterior left lateral absent, and the anterior obsolete, other teeth normal ; 

 sinus free, ascending obliquely; internal radii thick and strong but ill- 

 defined ; sculpture concentric, usually smoothish or not sharply lamellate, 

 sometimes reduced to incremental lines. Warm, temperate, and tropical 

 seas." Dall, 1900.' 



TELLINA (ARCOPAGIA) GEORGIANA Gabb 



Tellina (Tellinella) georgiana Gabb, 1876, Proc. Acad. Nat. Sci., Phila., p. 



307. 



Tellina georgiana Johnson, 1905, Ibidem, p. 16. 

 Tellina georgiana Weller,1907, Geol. Survey of New Jersey, Pal., vol. iv, p. 



615, pi. Ixx, figs. 1, 2. 



1 Trans. Wagner Free Inst. Sci., Phila., vol. iii, pt. v, pp. 1006-9. 



2 Dall, Trans. Wagner Free Inst. Sci., Phila., vol. iii, pt. v, p. 1011. 



