1936] Schults: Keys to Fishes 207 



Nape. Upper part of the neck, next to the occiput. 



Nares. Nostrils, anterior and posterior. 



Nasal plate. Plate in which the nostrils are inserted. 



Neural arch. The dorsal arch of a vertebra for the passage of the 



spinal cord. See neural spine. 

 Neural canal. The cavity of the neural arch as a whole. 

 Neural processes. Two plates rising vertically, one on each side of 



the centrum of the vertebra, which unite toward their ends 



and form a spine. 

 Nictitating membrane. The third or inner eyelid. 

 Nuchal. Pertaining to the nape or nucha. 

 Nuchal spine. Posterior to and in line with the parietal spine (at 



posterior edge of parietal ridge) occurs the nuchal spine. If 



one of these spines is absent it is the nuchal spine. 



Obsolete. Faintly marked, scarcely evident. 



Obtuse. Blunt. 



Occipital. Pertaining to the occiput. 



Occipital condyle. That part of the occipital bone modified to ar- 

 ticulate with the atlas. 



Occiput. Back of the head. In fishes, specifically the cross line sep- 

 arating the fleshy nape from the head. 



Ocellate. With eye-like spots, generally roundish and with contrast- 

 ing borders. 



-oid (suffiix). Like; as percoid, perch-like. 



Opercle or operculum. Gill cover; the posterior membrane bone of 

 the side of the head, in fishes. 



Opercular flap. Prolongation of the upper posterior angle of the 

 opercle. 



Opisthocoelian. Concave behind only, said of vertebrae with ball and 

 socket joints. 



Opisthotic. A bone of the skull with which the lower limb of the 

 posttemporal usually articulates. 



Orbicular. Circular. 



Orbit. Eye socket, (see length of eye). 



Origin of fin. The term applied to where the median fins begin on 

 the body. 



Osseous. Bony. 



Otolith. A bone of the inner ear of fishes lying in the sacculus. 



Oviparous. Producing eggs which are developed and hatched after 

 exclusion from the body, as in all birds and most fishes. 



Ovovoviparous. Producing eggs, usually with much yolk. Usually 

 hatching occurs before exclusion. 



Ovum. Egg. 



