CARDIACEA. MOLLUSCA. CARDIUM. 89 



therefore, not a little remarkable, that a shell so long ago observed 

 should have remained, until very lately, undescribed. But it is 

 only recently that it has been recognised as a distinct species 

 and described by Colonel Totten. It is commonly regarded as 

 the fry of the quahog (V. mercendria,) on account of its purple 

 tip. But on close examination it will be found to be a fully de- 

 veloped, mature shell, different in every important particular from 

 that species. It is a very interesting shell, as being by far the 

 least of any species of the genus known. 



Family CARDIACEA, Desk. 



Shell somewhat heart-shaped ; cardinal teeth two or three ; lateral teeth one 

 or two. 



GexNus CARDIUM, Lin. 



Shell somewhat heart-shaped ; beaks prominent ; margin gener- 

 ally toothed or folded within ; hinge icith two oblique cardinal and 

 two lateral teeth in each valve ; palleal impression without a sinus. 



Ca'rdium Isla'ndicum. 



Shell large., rounded-ovate^ tumid, sub-equilateral, with about 

 thirty-six sharp, three-sided ribs ; epidermis lax, and rising into a 

 fringe, on the angle of the ribs. 



Figure 58. 

 State Coll., No. 190. Soc. Cab., No. 1924. 



Cardium Islandicum, Lin; Syst.JVat., 1124. Chemn. ; vi. 200, t. 19, f. 195, 196. 



Gmelin ; Sijst., 2252. Brug. ; Encyc. Meth.,^2. Wood; Gen. Conch., 22o, pi. 



55, f. 2, 3. Index, pi. 5, f. 27. Lister; Conch., t. 329, f. IGG. Gualt.; 



Test., I. 71, f. M. K.NORR ; D6lices, S^-c, vi. t. 8, f. 3. Born ; Mus., 49. 

 Cardium ciiiatum, O. Fabr.; Fauna Grant., 410. 

 Cardium pubescens, Codthouy ; Bost.Journ. JVat. Hist., ii. 60, pi. 3. f. 6, (young.) 



Shell large, rather thin, nearly equilateral, a little obliquely 

 rounded-ovate ; tumid ; anterior side shortest and narrowest, 

 ends regularly rounded ; beaks prominent, the points turned in- 

 wards, and nearly in contact ; in front of them is a narrow, heart- 

 shaped depression ; on each valve are thirty-six, or more, three 

 sided, sharp-edged, radiating ribs, the furrows between themround- 

 12 



