Fishes of the JVestern North Atlantic 519 



operculum supported by a fan of slender cartilaginous rods, some fused basally to 

 form a thin disc connected with ceratohyal cartilage, others borne directly on latter. 

 Cartilaginous support for first dorsal fin a vertical plate to which dorsal spine is 

 firmly attached; this plate articulated with a projection from upper side of vertebral 

 column." Second dorsal fin supported basally by a series of numerous short rod-like 

 radial cartilages edged outwardly by a longitudinal ligament. Basal parts of pectoral 

 fins supported by a fan of numerous cartilaginous rods, divided transversely into several 

 series (allowing for motion) and borne basally by a cartilaginous element corresponding 

 to the metapterygial cartilage of elasmobranchs; also two other basal cartilages seemingly 

 corresponding to elasmobranch propterygial and mesopterygial cartilages, but these not 

 bearing radials among chimaeroids. Cartilaginous skeleton of pelvic fins similar to that 

 of pectorals, but only one basal cartilage, and radials shorter, with only one transverse 

 articulation. Anal and caudal fins without radial cartilages, supported by double series 

 of slender horny rays, as are outer parts of dorsal, pectoral and pelvic fins. Pectoral 

 girdle not joined above to vertebral column but attached to dorsal musculature'* by 

 a slender suprascapular cartilage on either side. The two halves of pelvic girdle united 

 below in midline by a ligament only, each end prolonged beyond point of articulation 

 of pelvic fin as a so-called "iliac" process running upward so that pelvis (like pectoral 

 arch) is suspended above from dorsolateral musculature of trunk without direct connec- 

 tion with vertebral column. Transverse (pubic) portion of each half of pelvis pierced by 

 an aperture covered over by membrane, or pierced by two apertures in some. The three 

 rostral cartilages rod-like, one articulated to front of cranium above, the two others 

 articulated lower down to nasal capsules. (In such Sharks as have three rostral cartilages, 

 the unpaired one is lowermost, the pair uppermost.) Cranium much compacted, the 

 anterior portion greatly compressed sidewise in most, with a relative increase in vertical 

 height as compared with elasmobranch cranium. No anterior fontanelle, the space be- 

 tween and behind olfactory capsules bridged over by cartilage. The orbits lie above the 

 level of the brain case in some, in which case the two orbits are separated one from the 

 other by a vertical membranous partition only;'^ in others the orbits are on a level with 

 the brain case from which each is separated by a membrane alone. ^'' Posterior part of 

 brain cavity high, anterior part low, tunnel-like, separated above by a horizontal partition 

 of cartilage from a similar cavity containing branches of the trigeminal (5th) nerve. 

 Auditory capsules not separated from brain cavity; greater part of membranous laby- 

 rinth of inner ear lodged in pits in lateral walls of cranium, separated from brain cavity 

 by membranes only. Posterior face of cranium articulated to vertebral column by a 

 saddle-shaped condyle, concave from front to rear but convex dorsoventrally, with an 

 additional flat condyle surface above it on either side. Most anterior vertebral segments 

 (dozen or so) fused together under first dorsal fin into a continuous tube, its segmental 



17. The first dorsal fin has two or three basal cartilages in some fossil chimaeroids. 



18. The chimaeroids resemble the Sharks in this respect and differ correspondingly from the Skates and Rays in which 

 the pectoral girdle is attached above to the vertebral column. 



19. Chimaeridae and Rhinochimaeridae. 20. Callorhinchidae. 



