46 



PISCES 



Family 3. Myriacanthidae. Smitli Woodward. 



Trunk elongated. Two upper pairs and one lower pair of thin dental plates, 

 also a stout, median, incisor-like tooth at the symphysis of the mandible. Head with 

 a few dermal plates. Males with a prehensile spine on the snout. Anterior dorsal 

 fin above the pectorals, tvith a long, straight, robust spine. Jurassic. 



Myriacanthus, Ag. (Prognathodus, Egerton ; Metopacanthus, Zittel). Eostrum 

 with a terminal cutaneous flap. Anterior upper dental plate smaller than the 

 posterior plate. Dorsal fin spine long and slender, somewhat laterally com- 

 pressed, with a large internal cavity ; sides ornamented with small tubercles ; 

 a series of large, thorn -shaped tubercles arranged along each edge of the 

 flattened posterior face, passing into a single median row distally, and a single 

 series of similar denticles on the anterior border. Eostral spine elongated 

 and pointed, with expanded base. Dermal plates tuberculated. M. paradoxus, 

 and M. gramdatus, Ag., from Lower Lias of Lyme Regis. 



Chimaeropsis, Zittel (Fig. 91). Mandibular dental plates (md), slightly 

 arched, with a large tritoral area ; the symphysial tooth (x) externally 



Ao- 



Chimaernpsls jiuradoxa, Zitt. Upper Jurassic (Lithographic Stone); Eichstadt, Bavai'ia. 1/2 u^t. size. 

 md, MaudibuUir tooth ; )), Hindei- upper tootli ; v, Anterior upper tooth in side view ; yi, Same from lower 

 side ; x, Slender premandibular tooth. 



(infei'iorly) convex, internally (superiorly) flat or concave. Anterior (v) and 

 posterior (p) upper dental plates triangular, the former not smaller than the 

 latter, and tapering in front, the latter tapering behind. Fin spine as in 

 Myriacanthus. Body covered with small, conical, radiately grooved placoid 

 scales. Upi)er Jurassic (Lithographic Stone) of Bavaria. 



Fauiily 4. Chixxiaeridae. Chiniaeras.^ 



Trunk elongated, shark-like. Teeth forming two piairs of robust dental plates in 

 the upper jaw, the foremost the smaller, both pairs thickened and closely apjjosed in 

 tJie longitudinal mesial line of the mouth ; lower dentition comprising a single pair of 

 beak-shaped plates meeting at the symphysis ; the plates usually with several tritors. 

 Pectoral fns very large, fan-like, with simple, horny rays; anterior dorsal fin above 

 the pectorals, with a large spine artictdated to a cartilaginous base ; posterior dorsal 



1 yeiiiOH. E. T.. The Cliiinaeroiil Fishes of the British Cretaceous Rocks (Mem. Geol. .Survey, 

 Mon. No. IV.), 1878. 



