376 



Occipital furrow — the transvei'se gToove on the cephaloii of 

 Trilobites, which separates the last, or occipital, i-iiig,- tVoni 

 the rest of the cephalon. 



Occipitii] ring — the posterioi- division of the glabella of a 

 Trilobite cephalon. 



Operculiforni — resembling an opercnlnni. 



Operculum — a lid or cover. 



PiiUial line — the line on the interior of the shell of niollnscs, 



marking the attachment of the mantle. 

 Pallial sinus — the reentrant angle in the pallial line, usually 



at the posterior end of the shell of Pelecypods ; it marks 



the attachment of the siphon muscles. 

 Palmnrs — the third series of brachial plates of the Crinoidea, 



lying above the axillary distichals. 

 Pn hnn to — pal m -sha |)ed . 

 Palpebnil lobes — the supra-orbital extensions from the fixed 



cheeks of Trilobites. 

 Papillose — covered with papillae or fine projections. 

 Parabasals — the second cycle of basal plates in Crinoids. 

 Pedicle — the fleshy peduncle or stem used for attachment in 



the Brachio})oda. 

 Periderm — the outer chitinous covering of Hydrozoa. 

 Periostracum — the epidermis or outer organic coating of 



shells. 

 Peristome — the margin of an aperture, /. e., the mouth of a 



uni^'alve molluscan shell, the mouth of a Bryozoan cell, 



etc. 

 Peritlieca — the epithecal covering which sui-rounds a colony 



of Corallites, i. e., a compound corallum. 

 Pinnies — the finest divisions of the arms of Crinoids. 

 Plano-convex — normally in Brachiopods, with the pedicle 



valve convex and the brachial valve flat. 

 Pleune — the lateral portions of the thoracic i-ings of 



Trilobites. 

 Polyp — the animal of a simple Coelenterate or Bryozoan. 

 Polypite — the individual polyp of a colony. 



