55 American Kast Coast Arcas 55 



Area rustica Tuomcy and Holmes 



Plate XIII. Figures 4, 5 



Ana ntslica Tuoniey and Holuies, Pleioc. Fos. S. Car., p. 39, pi. 15, iig. i, 1857. 

 Not A. rustica Contejean, 1859 (fide Dall). 



Scapharca (Area) rustica Conrad, Acad. Nat. Sci. Phila., Proc. for 1862, p. 580, 1863. 

 Area crassicosta Ileilprin, Wagner Free Inst. Sci., Trans., vol. i, p. 96, pi. 13, fig. 30, 1887. 

 Area crassicosta Dana, Man. Geol., 4th. ed., p. 900, fig. 150S, 1S95. 



Scapharca (Aiiailara) rustica Dall, Wagner Free Inst. Sci., Traus., vol. 3, p. 653, pi. 31, figs. 6, 9, 

 1898. 



"A. testa crassa. sub-quadrata, radiatim costata; costis sub-squamosis; latere buc- 

 cali brevioribus, costis crenatis; latere anali carinato, angulato, truncate, costis majori- 

 bus; umbonibus inter se fere contingentibus. 



"Shell thick, somewhat square, radiately, and unequally ribbed; ribs almost squa- 

 mose; buccal side very short, ribs crenate; anal side carinate, angular, tnmcate, ribs 

 very large; ligament area narrow, umbones nearlj^ touching. 



"This fossil is readily distinguished by the coarse ribs and deeply excavated inter- 

 stices on the anal side. The margin is strongly crenulated * * *." — Tuomey and 

 Holmes, 1857. 



"The collection of more material since Professor Heilprin's publication leaves no 

 doubt whatever as to the identity of this splendid species with that of Tuomey and Holmes. 

 It seems to be characteristic of the southern Pliocene. The beaks are much incurved 

 and distinctly prosocoelous, the cardinal area short and wide in front of them, long and 

 narrow with much elevated margins behind; the anterior part of the area is transversely 

 grooved at right angles to the hinge-line; the posterior part has converging grooves, thus 

 forming three or four concentric triangles. The hinge is composed of a short anterior 

 and long posterior series of subequal vertical teeth vertically striated on their flat sur- 

 faces; there are over forty teeth, of which twelve are anterior; the two series are closely 

 approximated. Many of the specimens have a strong posterior auriculation which is 

 more prominent in the young; one specimen measures thirty- two millimeters on the 

 hinge-line and twenty-eight millimeters below the auriculation. An adult measures 

 fifty-three millimeters long, thirty-six millimeters high, and forty millimeters in diame- 

 ter. The largest valve obtained is seventy-one millimeters long and has fifty-four pos- 

 terior and seventeen anterior teeth. In this specimen there are nine longitudinal 

 grooves, and the three or four middle ones are extended in front of the beaks, contrary 

 to the rule in younger specimens, giving the grooved area as a whole the form of a 

 long, narrow "stemmed" arrow-head. In this valve the hinge-line is sixty millimeters 

 long and the vertical of the beak is ten millimeters from the anterior end. 



"On the whole, this is one of the finest and most striking species in our whole Ter- 

 tiary fauna." — Dall. 



Ribs seventeen to twenty-two, large and coarse near the umbonal ridge, smaller and 

 more closely set anteriorly and posteriorly. Several Old World fossil species have been 

 called A. rustica since Tuomey and Holmes used the name. 



Pimnisions. — (Small valve), Ion. 4 10,-36 ; alt. -(-5,-29; seraidiam. iS mm. 



