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transverse, flattened, external facets, one straight, the other obliquely inclined; 

 hinge without teeth; a conical cardinal pit, situated below the beaks, partly 

 internal, opening outwards, and receiving the ligament. 

 10 fossil species. 



Pecten. Shell free, regular, inequivalve, auriculated; the lower margin 

 transverse, straight; beaks contiguous; hinge without teeth, a cardinal, trian- 

 gular pit, wholly internal, receiving the ligament. 



P. maximus, 

 ' medius, 

 ' Jacobseus, 

 ' bifrons, 

 ' ziczac, 

 ' Laurentii, 

 ' pleuronectes, 

 ' oblitevatus, 

 ' Jnponicus, 

 ' Magellanicus, 

 ' purpuratus, 

 ' lineolaris, 

 ' radula, 

 ' rastellum, 

 ' turgidus, 

 ' flagellatus, 



aspersus, 

 flavi'dulus, 



plica, 



glaber, 



sulcatus, 



virgo, 



unicolor, 



griseus, 



distans, 



isabella, 



nodosus, 



pallium, 



pes felis, 



tigris, 



imbricatus, 



histrionicus, 



sauciatus, 



opercularis, 



lineatus, 



flabellatus, 



irradians, 



flexuosus, 



inflexus, 



dispar, 



quadriradiatus, 



Islandicus, 



asperrimus, 



senatorius, 



aurantius, 



florens, 



P. varius, 



' sanguineus, 



' sinuosus, 



' ornatus, 



' pellucidus, 



' Tranquebaricus, 



' gibbus, 



' rainiaceus, 



' pusio, 



' hybridus, 



' sulplmreus, 



' lividus, 



' hexactes, 



' muscosus, 

 27 fossil species. 



Plicatula. Shell inequivalve, not auriculated, attenuated towards the 

 base, the superior margin rounded, subplicate; the beaks unequal, and without 

 an external facet; hinge having two strong cardinal teeth in each valve; a pit 

 between them, receiving the ligament, which is wholly external. 



P. australis, 6 fossil species. 



P. ramosa, 

 ' depressa, 



P. cristata, 

 ' reniformis, 



Spondylus. Shell inequivalve, adhering, auriculated, echinated or rough, 

 the beaks unequal, the lower valve having an external, flattened, cardinal facet, 

 divided by a channel which lengthens with age; hinge having two strong 

 teeth in each valve, and an intermediate pit for the ligament, communicating 

 by the base with the external channel. Ligament internal; the remains of 

 former ligaments are seen outside in the channel. 



S. gsedaropus, 

 ' Americanus, 

 ' araclinoides, 

 ' candidus, 

 ' multilamellatus, 

 ' costatus, 



S. variegatus, 

 ' longispina, 

 ' regius, 

 ' avicularis, 

 ' coccineus, 

 ' crassisquama, 



S. spathuliferus, 

 ' ducalis, 

 ' longitudinalis, 

 ' microlepas, 

 ' croceus, 



S. aurantius, 



' radians, 



' zonalis, 



' violacescens, 

 4 fossil species. 



