PAT.AKONTOfiRAPHICA AmKRICANA 62 



Not ^ica americana Orb., Moll. Cuba, 2, p. 317, pi. 2S, figs, i, 2, 1S53. 



Scapharca {Argina') campechensis Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, pp. 650, 659, 

 189S. 



"Shell ovate-heart-shaped, with longitudinal ribs, and crowded transverse striae; 

 margin crenated * * '■'■. 



"Shell about an inch and a quarter long, and an inch and three quarters broad; 

 white, tinged with flesh colour at the margin and summits ; it has about twenty- 

 five longitudinal ribs, which are crossed with crowded imbricated striae, and 

 at first sight has more the appearance of a Cardiiun than of an Area." — Dill- 

 -u'yti, 1817. 



Shell inequivalve, nearly round to rounded quadrate, with much incurved beaks 

 which nearly touch so that the posterior part of the cardinal area appears lens shaped 

 from above; ribs twenty-six to thirty-seven, square on the right valve, often rounded 

 on the left, especially on the posterior part of the shell; ribs usually as wide as or wider 

 than the interspaces; ribs of the left valve often, and of the right valve sometimes with 

 a median groove, sometimes practically all the ribs of both vahxs are grooved, some- 

 times httle grooving on either valve, the species is very variable in this respect, but the 

 grooving is usually stronger on the left valve; beaks very far forward; hinge-line some- 

 what curved; posterior series of teeth long, teeth oblique distally, v-shaped near the 

 middle of the series; anterior series short, broad and irregular; cardinal area long and 

 ven.' narrow posteriorly, wider and very short anteriorly ; margin fluted. 



Although this species varies widely in form and ribbing it is easily distinguished 

 from other east coast species by its hinge and cardinal area. 



"This very interesting species, of which the synonymy might be much extended, af- 

 fords an excellent illustration of the effects of environment upon the recent form. Its 

 northern limit is at Cape Cod, where the shell is often large, always coarse, and with a 

 dense hirsute periostracum * '^ *. As we proceed southward, in this species, as in many 

 other shells, we find the shell becoming less earthy and more porcellanous, the sculpture 

 more neat, the periostracum less profuse, and the general size less. South of Cape Hat- 

 teras the chalky, thin type, common in the north, is seldom if ever found. In the Gulf 

 of Mexico and the Antilles the shell is still smaller than in the Carolinas * * *. A 

 somewhat similar series of differences is observable in the Pleistocene fossils, though less 

 pronounced. 



"GmeUn's description was inadequate, and only identifiable by his reference to 

 Lister. The species was elucidated by Dillwyn ■'■• ='■' ■'. 



"The typical A. campechevsis is the rounded southern form which Stimpson after- 

 wards called A. Holmesii, as he himself recognized. Say's description of ^4. /if.ra/a in- 

 cluded all the varieties of our eastern coast, but Gould first described the shell so as to 

 make this name apply more particularly to the somewhat elongated, earthy northern va- 

 riety. Gray's A. americana was founded on a very elongated, more porcellanous form, 

 such as is common in South Carolina waters. The study of a large series of recent spe- 

 cimens, ranging from Jamaica to Cape Cod, obliges me to recognize that no sharp line of 

 discrimination can be drawn between the several varieties. The number of ribs varies 



