i;R P.M.AHONTOfJRAPHICA A^rKKICANA 58 



Area scalarina Hcilprin 

 Plate XIII, Figure 12; Plate XI\', Figures i, 2, 3 



Area %calari>ia Ileilpriu, Wagner Free Inst. Sci., Trans., vol. i, p. 94, pi. 12, fig. 29, 1887. 

 Scapharca {Cuuearca) scalarina Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 634, 1898. 



"Shell obliquely rhomboidal, elevated, ventricose, angulated posteriorly, flattened ; 

 anterior end short, evenly rounded; beaks prominent, transverse, about eight, distant; 

 ligament-area diamond-shaped, nearly smooth in the young shell, with delicate transverse 

 lines — in the adult, with a limited number of coarse, sinuous longitudinal lines; hinge- 

 line straight, somewhat more than one-half the greatest length of shell; teeth numerous, 

 somewhat oblique toward either end. 



"Ribs prominent, about twenty-four, broad, square, robustly crenate, those of the 

 left valve broader than the interspaces, flattened posteriorly, about eight on the anal 

 angulation; those of the right valve of about the same width as the interspaces (tlie an- 

 terior ones the broadest), with an interstitial secondary rounded rib in the center of the 

 interspace: the two valves unequal, the basal margin of the left vah-e greatly protruding 

 beyond that of the right; base profoundly crenulated. 



"Length, 3.3 inches; height, 2.5 inches. 



":^ * * It closely resembles the shell identified by Tuomey and Holmes with Area 

 scalaris of Conrad •■■ * *. Through the kindness of Prof. Whitfield I have been per- 

 mitted to make a comparison ■with the type-forms described and figured by Tuomey and 

 Holmes, and find that their shell differs verj- materially from the Florida fossil. In the 

 first place it is decidedly more oblique, and secondly, the ribs adjoing the posterior slope 

 (on the left valve) are not nearly as broad relatively, nor as flattened, as they are in 

 A. scalarina: the ribs of the left valve are more remotely placed from one another, and 

 lack the pronoimced interstitial secondary rib, which is so prominently defined in the 

 Florida fossil. Its ijlace is taken by a hair line, which is present in some of the inter- 

 costal spaces. The characters of the Florida shell are remarkablj'- constant * * * and 

 were I as positive of the stability of characters of the Carolina fossil, I should have no 

 hesitation in regarding the two as specifically distinct '■'■■ '-'■'■ '■'■''. As it is, the characters of 

 the two are sufficiently distinct, indeed, fully as well-marked as those which separate 

 the Florida fossil from the recent Area incongiua of the Southern coast, which may, with 

 much plausibility, be looked upon as its immediate descendant. The recent species 

 agrees more nearly in the general outline of the shell, being upright rather than oblique, 

 but differs in the less width (in the left valve) of the ribs, and in lacking the true inter- 

 stitial rib of the right valve (although an indication of it appears in a faint elevated 

 line), agreeing in this respect with the South Carolina fossil. That the three forms are 

 most intimately related there can be no question, and I believe there is likewise little or 

 no question that all lie on the same line of descent." — Hcilpri)/. 1887. 



"This magnificent species is the largest and most distinct of the entire group, and 

 so far has been obtained only on the Caloosahatchie River * ■>= *." — Dall. 

 Ocrurrencf.—'PWncenem^vXf. of the Caloosahatchie, Florida.— A?//. 



