ARCADE. 21 



ARC A PONDEROSA. 



Plate IV. Figs. 4 and ia. 



Area ponderosa, Say, Jour. Acad. Nat. Sci., Vol. 2, p. 267. 



Area ponderosa, De Kay, Zool. New- York, Art. Mollusca, p. 177. 



Area ponderosa, Ravenel, Cat. Coll. Shells, p. 5. 



Area ponderosa, L. R. Gibbes, Tuomey's Geol. So. Ca., appendix, p. xxi. 



Area ponderosa, Say's Conch. U. S., (Binney,) p. 92. 



Description. Shell thick, ponderous, obliquely-oblong, with thirty to thirty-five ribs; 

 those on the posterior half, impressed with a line or groove ; anterior ribs without lines ; 

 interstitial spaces equal to width of ribs ; buccal margin thick, rounded ; anal margin 

 angularly produced, obliquely truncated, thin ; pallia! margin contracted in the middle ; 

 ligamental area wide, crossed with prominent lines or ridges, corresponding to the teeth ; 

 umbones prominent, remote. 



A. ponderosa is a Southern coast shell, and very abundant in the Post-Pleiocene. 



Plate IV. Fig. 4, Shell, natural size. 

 " 4a, Hinge view. 



Locality. Charleston; Simmons'. 



Museum, College of Charleston; Cabinet F. S. H. 



ARCA TRANSVERSA. 

 Plate IV. Figs. 5 and 5a. 



Area transversa, Say, Jour. Acad. Nat. Sci., Vol. 2, p. 269. 



Area transversa, Con., Foss. Shells Ter. Form., No. 2, p. 15, tab. 1, fig. 2. 



Area transversa, Gould, Invert. Mass., p. 96. 



Area transversa, Ravenel, Cat. Coll. Shells, p. 5. 



Area transversa, L. R. Gibbes, Tuomey's Geol. So. Ca., appendix, p. xxi. 



Area transversa, Tuomey 4- Holmes, Pleiocene Foss. So. Ca., p. 42, pi. 15, figs 6 and 7. 



Area transversa, Stimpson, Shells New-England, p. 8. 



Area transversa, Say's Conch. U. S., (Binney,) p. 93. 



Description. Shell transversely oblong, sub-rhomboidal ; buccal side shorter, regularly 

 rounded, angular above; anal side elongated, angular; ligamental area narrow, furrowed; 

 6 



