12 CARDIADiE. 



synonymy : we have preferred, then (since one or the other 

 name must he expunged), the preservation of that which 

 we have ascertained to he correct. ^^ 



This large species is of a somewhat rounded heart-shape, 

 and is usually oblique, but varies much in outline from the 

 greater or lesser flattening of the hinder dorsal area, which 

 being rounded in the young, the contour is then rather 

 square, but becomes occasionally subtriangular in the aged, 

 from the hinder compression so usual at that stage of 

 growth. The valves are very tumid, opaque, solid, and 

 often ponderous ; the convexity is evenly diiFused, being 

 most manifest subcentrally, and then gradually diminishing 

 towards the sides and lower margin. The external surface, 

 which is somewhat glossy, and tinged with rufous or reddish 

 brown, occasionally adorned with deeper zones of the same 

 hue, is rayed with about twenty-two strong ribs, which 

 are separated, except in front, by interstices of at least 

 equal breadth to them. The ribs are broad, well raised, 

 somewhat square-topped, and armed with rather close-set, 

 unconnected small knobs or tubercles, which, in full-grown 

 perfect individuals, are present on all of them, and occupy 

 the middle of their surface only, becoming more pointed 

 on the posterior ones, and more obtuse large and broad on 

 the anterior ones. The interstitial spaces, which are pro- 

 portionately narrower in front, are concentrically ti'aversed 

 by most crowded and irregularly-flexuous narrow ridges 

 or elevated sulci, which likewise ascend the sides of the 

 ribs, and in the younger examples actually surmount them. 

 The tubercles (which, in a variety now before us, are large 

 and spinous, but not, as in echinatmn, laterally com- 

 pressed and radiatingly linked to each other) are usually 



* For a more detailed account of the Cardium tuberculatum of Linnasus, see 

 the " Ipsa Liiina;i Conchylia'' of Mr. Hanley, now in preparation for the press. 



