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Occipital furrow — the transverse groove on the cephalon of 

 Trilobites, which separates the last, or occipital, ring- from 

 theresl of the cephalon. 



Occipital ring — the posterior division of the glabella of a 

 Trilobite cephalon. 



Operculiform — resembling an operculum. 



Operculum — a lid or cover. 



Pallial line — the line on the interior of the shell of molluscs. 



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. 

 Palmars — the third series of brachial plates of the Crinoidea. 



lying above the axillary distichals. 

 Palmate — palm-shaped. 

 Palpebral lobes — the supra-orbital extensions from the fix^d 



cheeks of Trilobites. 

 Papillose — covered with papillae or fine projections. 

 Parabasals — the second cycle of basal plates in Oinoids. 

 Pedicle — the fleshy peduncle or stem used for attachment in 



the Brachiopoda. 

 Periderm — the outer chitinous covering of Hvdrozoa. 

 Periostracum — the epidermis or outer organic coating of 



shells. 

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



univalve molluscan shell, the mouth of a Biwozoan cell. 



etc 

 Peritlieca — the epithecal covering which surrounds a colony 



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

 Pinules — the finest divisions of the arms of Oinoids. 

 Plano-convex — normally in Brachiopods, with the pedicle 



valve convex and the brachial valve flat. 

 Pleurae — the lateral portions of the thoracic rings of 



Trilobites. 

 Polyp — the animal of a simple Coelenterate or Bryozoan. 

 Polypite — the individual polyp of a colony. 



