SUB-CLASS I 



SELACHII 



37 



(Fig. 73). Head and back covered with longitudinal series of tuberculated or 

 spiny, partially keeled placoid scales 



A 



and small shagreen granules. On each 

 side of the front portion of the head 

 a triangular spine, provided with a 

 broad, hollow base and covered with 

 tubercles of dentine. Further back 

 on each side three smooth, thin, arched 

 spines fixed by a conspicuous basal 

 process in the skin of the head, curved 

 inwards, and apparently consisting of 



calcined Cartilage ; the middle pair 01 Zittel). Dentition from above {A), and below (B), nat 

 ,i ,i • ■, size. Kupferschiefer ; Glucksbrunn, Thurineia. 



these spines more than twice as long 



as the others. Dentition consisting of one pair of Cochliodont teeth in each 



jaw (Fig. 73). M. armata, Ewald, from Kupferschiefer of Germany. 



Pig. 73. 

 Menaspis armata, Ewald (Chalcodus permianus, 



Family 2. Psammodontidae. De Koniiuk. 



Known only by large, flat, or slightly arched teeth, with punctate or finely rugose 



grinding surface. The teeth are of quadrate or oblong shape, 

 and were originally arranged in one, two, or more longitudinal 

 series. Lower Carboniferous. 



Psammodus, Ag. (Homalodus, Astrabodus, Davis), 

 (Fig. 74). Teeth quadrangular, with relatively thick 

 base, smooth or feebly striated on the attached surface, 

 arranged in the jaw in paired longitudinal series. 

 P. rugosus, Ag. (Fig. 74), from Carboniferous Limestone 

 of Ireland, Scotland, England, Wales, and Belgium. 

 Allied species in Russia and North America. 



A rchaeobatis, Newberry. Teeth scarcely distinct 

 from Psammodus. An associated group of A. gigas, 

 Newb., known from St. Louis Limestone, Greencastle, 

 Indiana (Ann. New York Acad. Sci. vol. i. 1878, p. 190). 



Copodus, Davis (Mesogomphus, Ehymodus, Characodus, 

 Pinacodus, Davis). Comparatively small median teeth, 

 narrower in front than behind, divided into two unequal 

 parts by a transverse suture. C. cornutus, Davis, and 

 allied species from Carboniferous Limestone of Ireland, 

 England, and North America. 



Fig. 74. 



Psammodus rugosus, Ag. 

 Imperfect tooth from above 

 (A), and in transverse section 

 (B), nat. size. Carboniferous 

 Limestone ; Armagh. 



Family 3. Petalodontidae. Newberry and Worthen. 



Teeth aider o-posteriorly compressed, transversely elongated, arm aged in longitudinal 

 and transverse rows and forming a pavement. Crown enamelled, more or less bent 

 backwards, either with a sharp cutting edge or very obtuse, the anterior face convex, the 

 posterior face concave ; root separated from the crown by a constriction, usually with 

 enamel folds immediately above it. Carboniferous and Permian. 



Of this extinct family, Janassa is the only genus of which more than the 

 dentition is known. This fish exhibits a ray -shaped trunk covered with 

 smooth, rounded shagreen granules ; the large pectoral fins extend forwards 



