29 



NUCULA. 



GENERIC CHARACTER. 



Shell equivalve, with contiguous beaks ; hinge 

 with an anterior and posterior series of numerous 

 teeth, interrupted at the summit by a triano^'lar car- 

 tilage fosset; ligament interior j muscular impressions 

 two. simple. 



OBSERVATIONS. 



Although Lamarck includes this genus in his family 

 */lrcacea, in a more natural arrangement it would pro- 

 bably be referred to Mactracea of the same author. 

 Turton first observed its affinity to Mactra ; and cer- 

 tainly the cartilage fossest which is so remarkable in 

 this genus, is wanting in Ai^ca and Pectunculus, 



Sowerby, in his Genera of Shells^ indicates three 

 divisions of this genus: 1st, of shells whose general 

 form is lanceolate, and have no epidermis; 2nd, of 

 shells which are rostrated, and have a strong epider- 

 mis. These constitute the genus Lembulus of Leach, 

 and Sowerby supposes that some of them at least may 

 be fresh water shells; the JV. limatula, however, one 

 of the largest and most beautiful of the JVuculse, be- 

 longs to this division, and is decidedly marine. The 

 3rd division consists of small obtusely ovate shells, 

 one of which, the Area nucleus of Linneus, is the 

 type of the genus, and although there is a striking 

 dissimilarity in outline between these and the shells 

 of the t'Ao former divisions-, the generic chai'acter is 

 essentially the some. 



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