SHARKS AND SKATES. 



71 



Sub-Class I. — Holocephali. 



The Chimaeras, though exceedingly bizarre in their ajipearance, liardly deserve the 

 name applied to the principal genus. Popularly, there is little of interest concerning 

 them, but to the naturalist they present many features to engage the attention. The 

 notochord persists, and tlie vertebraj are represented by a series of ossified rings in 

 the notocliordal sheath. The upper jaw is rudimentary, and firmly united to the skull, 

 while the lower is articulated to the long and slender hyomandibular. The jaws are 

 armed with four plate-like teeth above, and two below. The mouth is small and in- 



Fig. 57. — Chimcnra mmistrosa, clii 



ferior in position ; while above the eyes, in the male, is a c-ui-ious, erectile, stalked 

 appendage, spined at its extremity, of problematic character. The eyes are very large, 

 and are without lids; the skin of the adult is naked, but in the young there are a 

 number of small placoid scales on the back. In the skin, especially that of the head, 

 the neuro-epithelial system is well developed, and the lateral line is present. The gill- 

 clefts ar(^ four in numljor, but they open externally through a single opening which is 

 covered by a fold (.f the skin, slightly stiffened by cartilage. This rudimentary gill- 

 cover represents the well-develojied operculum of the Teleosts or true fishes. No 

 spiracle occurs. The fins, especially the ])eetorals, are well dcvelojied, while ' elas- 

 pers' occur in connection with the ventral fins of the male. Dr. B. (i. Wilder has 



