108 CLASS I. TROPIOPODA. ORDER I. BIMUSCULOSA. 



dentibus numerosis obliquis ; medianis ssepissime obsoletis. Liga- 

 raentum externum. Animal nunquam bysso affixum. 



The leading characters of Area are exhibited in this genus in a modified 

 form ; the shell being orbicular has the teeth set in a curved line, and 

 the umbones are much closer, with but a small area between them. 



The shell of Pectunculus is described as sublenticular, equivalve, 

 nearly equilateral, often covered with a hairy or downy epidermis, and 

 the umbones are but little separated ; the valves are always close shut, 

 and generally crenulated round the inner margin. The hinge, which is 

 curved, consists of a series of numerous small teeth, the middle of which 

 are very often obsolete. The ligament is external, and the animal never 

 has a byssus. 



Examples. 



PI. LXXXIII. Fig. 1. 



Pectunculus pilosus, Lamarck, Anim. sans vert., new edit., vol. vi. 



p. 488. Enc. Me'th., pi. 310. f. 2. 

 Area pilosa, Linnaeus. 



PI. LXXXIII. Fig. 2. (fossil.) 



Pectunculus pulvinatus, var. Lamarck, Anim. sans vert., new edit., 

 vol. vi. p. 496. Deshayes, Desc. des Coquilles fossiles, pi. 35. f. 15 

 to 17. 



NUCULA, Lamarck. 



Testa transversa, aut tenuis aut solida, aaquivalvis, insequilateralis, intus 

 interdum margaritacea, extus epidermide aut viridi aut fusco-oli- 

 vacea induta ; umbonibus contiguis, area intermedia nulla. Cardo 

 linearis, fovea mediana oblique producta ligamentum interne gerente ; 

 dentibus numerosis, acutis, subrecurvis, in seriem utrinque dispo- 

 sitis. Impressio muscularis pallii integra. 



