15S 



at the extremities, and furnished with numerous serial and entering teeth. 



Ligament wholly external. 



A. tortuosa, A. sulcata, A. cancellaria, A. inequivalvis, 



' semitorta, ' ovata, ' callifera, ' Indica, 



' Nose, ' barbata, ' irudina, ' senilis, 



' tetragona, ' fusca, ' Helbingii, * Brasiliana, 



' umbonata, ' Magellanica, ' scapha, ' corbicula, 



' sinuata, ' Domingensis, ' antiquata, ' squamosa, 



' avollana, ' lactea, ' rhombea, ' Cayennensis, 



' cardissa, ' trapezina, ' granosa, ' bisulcata, 



' ventricosa, ' pistachia, ' auriculata, 9 fossil species. 



' retusa, ' pisolina, 



Pectunculus. Shell orbicular, 

 eral, close; hinge arched, furnished 

 teeth; those in the middle obsolete, nearly obliterated 



almost lenticular, equivalve, subequilat- 

 with numerous serial, oblique, entering 



P. glycimeris, 

 ' pilosus, 

 ' undulatus, 

 ' marmoratus, 

 ' scriptus, 



P. pennaceus, 

 ' rubens, 

 ' angulaius, 

 1 stellatus, 

 ' pallens, 



P. violacescens, 

 ' zonalis, 

 ' striatularis, 

 ' nummarius, 

 ' castaneus, 



Ligament external. 



P. pectinatus, 

 ' pectiniformis, 

 ' radians, 

 ' vitreus, 



9 fossil species. 



Nucula. Shell transverse, ovate, triangular, or oblong, equivalve, inequi- 

 lateral; no facet between the beaks; hinge linear, broken, many toothed, in- 

 terrupted in the middle by an obliquely extending spoon-shaped pit; the teeth 

 numerous, often produced, as in the pectens; the beaks contiguous, curved 

 backwards. Ligament marginal, and partly internal, inserted in the pit or 

 spoon of the hinge. 



N. lanceolata, 

 ' rostrata, 

 ' pella, 



N. Nicobarica, 

 ' obliqua, 



N. lanceolata, (Sowerby, f. 1. 



elongata, 



tellinoides, 



crenifera, 



arctica, 



Nicobarica, 



curvirostra, 



Pella, 



glacialis, (Wood, Supp. pi. ii. f. 6. 

 fluviatilis, (Sowerby, Gen. 

 minuta, (Montague, 

 para, (Sowerby, C. 111. f. 7. 

 costellata, ' 



gibbosa, 

 eburnea, 

 polita, 

 nasuta, 



9. 

 10. 

 11. 

 12. 



