SUB-CLÄSS I 



SELACHII 



37 



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



spiny, partially keeled placoid scales ^ 



and small shagreen granules. On each 



side of the front portion of the head 



a triangulär 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 



calcified cartilage ; the middle pair of 



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. 



Fig. 73. 



Menaspis armata, 



Ewald (Chalcoilus permiaiius, 

 Zittel). Dentition froni above (A), and belovv (ß), nat. 

 size. Kupferschiefer ; Glücksbrunn, Thuringia. 



Family 2. Psammodontidae. De Koninck. 



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. 



Fsammodus, 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. 



Archaeobatis, Newberry. Teeth scarcely distinct 

 from Psammodus. An associated group of A. gigas, 

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

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



Copodus, Davis (Mesogomphus, Bhymodus, 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, An. 

 Iniperfect tooth from above 

 (A), and in transverse section 

 (B), nat. size. Carboniferous 

 Limestone ; Armagh. 



Family 3. Petalodontidae. Newberry and Worthen. 



Teeth anter o-posteriorly compressed, transversely elongated, arranged in longitwliruil 

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

 backwaras, 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 



