PISCES. 13 
6b. Gill opening single, leading to four gill clefts; jaws coalescent with the 
skull; a rudimentary opercle; teeth coalescent forming bony plates. 
(Chimeras.). . « . « « «+ © « « + HOLOCEPHALI, page 24. 
aa. Gills free, attached at base only to the gill arches; gill opening single on 
each side; eggs comparatively small aud numerous; no claspers; mem- 
brane bones present on head; cerebral hemispheres not united. (Ziue 
Fishes.) . . + 6 «© «© «© «© © + © © « «© TELEOSTOMI, page 25 
