CARDIUM. 23 



broad and rounded both above and below at its extremity. 

 The hinder termination is likewise broad, and very indis- 

 tinctly sub-biangulated, the lower angle being a right or 

 an obtuse one, and the upper being usually rounded off. 

 The luuular depression, when present, is very narrow : the 

 ligament is neither remarkable for size nor projection. The 

 umbones are not particularly j^rominent, and the beaks are 

 tolerably acute, and scarcely inclined forward. The colour- 

 ing of the inner surface is similar to that of the external ; 

 in a single immature specimen, however, from Guernsey, 

 which is of a pale pink without, the internal disk is of 

 a deep rose-colour. The lateral teeth are nearly equidis- 

 tant from the primary ones. A large specimen will occa- 

 sionally attain to almost half an inch in length, and a trifle 

 less in breadth ; but the majority of examples are of lesser 

 proportions. 



It is difficult to account for so generally diffused a spe- 

 cies having escaped observation until the publication of the 

 " Dithyra Britannica" of Dr. Turton ; since but little rea- 

 sonable doubt can be entertained that this is not the C. 

 nodosum of Montagu, which is described as being three 

 quarters of an inch in diameter, and of a flattened shape. 

 The language, indeed, of that author accords far better with 

 the young of tuberculatum, of which sj)ecies a tablet of im- 

 mature individuals, supposed to have once formed part of the 

 Colonel's collection, exists, thus named in our national 

 Museum. 



" Animal suborbicular, mantle white, open, clothed with 

 white pointed filaments, corresponding to the ribs of the 

 shell. The tubes are very short, pale yellow, each with 

 ten or twelve flaky white cirrhi at their extremities, and 

 red points at their bases, besides longer wavy white fila- 

 ments above and below, and on them. The anal orifice has 



