50 



FISH GALLERY. 



bears some resemblance to that of the Dipnoan. fishes (Lung-fishes) , 

 consisting of three pairs of tooth-plates (see 151), and the 

 upper jaw is confluent with the cranium, as in the Dipnoi (see 

 skull 148; also 154). The skin is soft and except in the extinct 

 genera has few dermal denticles. The skeleton is cartilaginous, 

 the notochord is persistent, and the calcified rings that occur in 

 its sheath are more numerous than the vertebral segments. The 

 marginal parts of the fins are supported by sheets of closely-set 



Rabbit- 

 fish. 



Fig. 27. — Rabbit-fish, Chimccra monstrosa. 



in., mouth ; n.p., nasal process, occurring in male only; op., operculum or 



gill-cover. (After Bridge, Camb. Nat. Hist., vii, 1904.) 



horny fin-rays. A spine is present in front of the first dorsal fin. 

 The tail is long and terminates in a filament. The gill-slits do 

 not open separately on the sides of the neck as they do in the 

 Elasmobranchii, but are crowded together beneath a gill-cover 

 (operculum), which is not supported by skeletal parts as it is in 

 bony fishes like the Cod and Mackerel. Spiracles are wanting in 

 the adult. There are valves in the conus arteriosus of the heart, 

 and a spiral valve in the intestine. The intestine opens separately 

 on to the exterior, and not into a common cloaca as it does in the 

 Elasmobranchii. The eggs are large and the egg-shells horny 

 (see 153). In addition to the pelvic claspers, such as occur also 

 in Elasmobranch fishes, the male Chimaeroids have a pair of 

 anterior claspers and a curious process arising from the snout 

 (fig. 27, n.p.). The subclass is an ancient one; dental plates 

 recognisable as those of Holocephali, and dorsal fin-spines 

 (ichthyodorulites) are found in rocks of Devonian age. 



Squaloraia (145) is an extinct Chimseroid, the remains of which 

 occur in the Lower Lias of Lyme Regis. The dentition is simpler than 

 that of the recent Holocephali, and the plates are much thinner. 



In Chimara (149, and fig. 27) the snout is bluntly conical, and 



