NUCULA 



TESTA ^equivalvis, insequilatera, transversa, 

 plerumque tenuis, epidermide induta. Cardo 

 linearis, fovea mediana oblique producta, liga- 

 mentum internum gerente, interuptus; denti- 

 bus lateralibus utrinque numerosis, acutis, sub- 

 recurvis, alternatim insertis. Umbones contigui. 

 Impressiones juusculares duae, simplices. Im- 

 pressio pallii adhaerentis museuli integra. 



Except in its nunlerOus teetli^ this Genus tias nothing 

 in common with Area and Peetuneulus/* is the first obser- 

 vation of Turton, in his ^' Conchylia insularum Britanni- 

 carum/' upon this Genus; an observation in no wise 

 according with those of Lamarck^ who has placed the 

 Nuculae next to the Pectunculi^ and who represents them 

 as truly related to the Pectunculi and Arcae, but still 

 eminently distinct ; and, forming hy the situation of the 

 ligament of their valves an evident transition to the 

 Trigonia:, he says, they unite these latter to the family of 

 the Arcaceae; but we find that the opinion of the last 

 mentioned author is partly founded in mistake, for in 

 describing it, he speaks of the ligament as being only 

 partly internal, whereas we find a scarcely distinguish- 

 able portion of it to be external, and it is well known that 

 no part of it is internal either in the other Arcacecsj or in 

 the Trigonice; so that we are strongly disposed to agree 

 with Turton and Leach, who placed Nucula in the san^e 

 family with Mactra, and as we discover no resemblance 

 between it and the Arcaceae, except in its numerous teeth, 

 we would separate it from them to unite it to the Mac- 

 traceae. Linne, in conformity with the principles upon 

 which his system was founded, placed it together with 



