146 



CARDIAD^. 



one and three fonrtlis of an inch, become solid and strong, and also 

 more tumid, especially behind. Tlie young shells often have the 

 surface variegated with stripes, or angular markings, of a rusty- 

 brown color. This species is also remarkable for gaping posteriorly 

 to a considerable extent. 



Oeniis CARDITA, Bruguieres. 1789. 



Shell inequipartite, regular ; hinge with a short, strong, erect 

 tooth under the beaks, and an oblique one stretching along the 



margni. 



Cardita borealis. 



Fig. 59. 



Shell obliquely sub-cordate, beaks prominent and recurved, with about twenty 



radiating ribs; 



margin crenate ; 



lunule small and deep. 



Tiff. 455. 



Cardita borealis, Coxrad, Amer. Mar. Conch. 39, pi. 8, fig. 1 (1831). — Reeve, Conch. 

 Icon. pi. 7, fig. .'jS. — De Kay, Nat. Hist. New York, 204, pi. 22, fig. 247. — Mid- 

 DEND. Siber. Reise, Moll. ii. 87; Beitr. z. Mai. Ro.ss. ill. 29. — Stimpson, Shells of 

 New England, 18. — Mighels, Shells of Maine, 16; Bost. Journ. Nat. Hist. iv. — 

 Gray, Zool. Beechey's Voy. 152, pi. 44, fig. 1. 



Arcturus nidis, Humphrey, MSS. 



Cardita vistita, Deshayes, Proc. Zool. Soc. pi. 17, fig. 10 (1852). 



Shell rounded, obliquely heart-shaped, thick and strong ; inequi- 

 partite ; the beaks elevated and turned forwards, so as almost to be 



even with the anterior extremity, which is 

 regularly rounded ; posterior margin regular- 

 ly rounded by a much larger curve, which, 

 meeting the base, forms an obtuse angle ; 

 surface raised into about twenty rounded, 

 radiating ribs, which are broader than the 

 grooves between them ; these are rendered 

 rougli by coarse lines of growth, and covered 

 by a strong, rusty-brown epidermis ; lunule 

 very strong, and deeply imprinted, rhom- 

 boidal ; ligament small and sunken, nearly concealed ; hinge strong, 

 two teeth in each valve ; in the left valve a small triangular one 

 under the licak, and an oblique, grooved, or partially double one 

 along the posterior margin as long as the ligament ; on the right 

 valve a long, tapering, oblique tooth, fitting beneath the two teeth of 

 the opposite valve, and a more slender one on which the ligament 

 partially rests ; interior white, margin strongly crenate ; impressions 



C. borealis. 



