166 



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, 



Jacobaeus, 



bifrons, 



ziczac, 



Laurentii, 



pleuronectes, 



obliteratus, 



Japonicus, 



Magellanicus, 



purpuratus, 



lineolaris, 



radula, 



rastellum, 



turgidus, 



flagellatus, 



aspersus, 



flavidulus, 



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, 



' miniaceus, 



' pusio, 



' hybridus, 



' sulphureus, 



' 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. ramosa, 

 ' depressa, 



P. cristata, 

 ' reniformis, 



P. australis, 



6 fossil species. 



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, 

 ' arachnoides, 

 ' candidus, 

 ' multilamellatus, 

 1 costatus, 



S. variegatus, 

 ' longispina, 

 ' regius, 

 ' avicularis, 

 ' coccineus, 

 ' crassisquama, 



S. spathuliferus, 

 ' ducalis, 

 ' longitudinalis, 

 ' microlepas, 

 ' croceus, 



S. aurantius, 



' radians, 



' zonalis, 



' violacescens, 

 4 fossil species. 



