SUB-CLASS I 



SELACHII 



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



spiny, partially keeled placoid scales ^ 



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 



Fig. 73. 

 Menas2ns armata, Ewalcl {Clialmdus permiamis, 



calcified cartilage ; the middle pair of ^ittel). Dentition from above (A), and below (B), nat. 

 ,1 . ,1 , ■ 1 size. Kupferschiefer ; Gliicksbnuin, Thuriiigia. 



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. 



Family 2. Psammodontidae. De Kouinck. 



Kno'ivn only hy large, flat, or slightly arched teeth, with punctate or finely rugose 

 J qrincling surface. The teeth are of quadrate or oblong shape, 



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

 series. Lower Carboniferous. 



Psammodus, Ag. {Homalodus, Astrahodus, 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 

 Allied species in Eussia and North America. 



Archaeobatis, Newberry. Teeth scarcely distinct 

 from Psammodus. An associated group of A. gigas, 

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

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



Copodus, Davis {Mesogomphus, Rhymodus, Characodus, 

 Pinacodus, Davis). ComjDaratively 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 L-eland, 

 England, and North America. 



Belgium. 



Fig. 74. 



Psariimodus rugosus, Ag. 

 Imperfect tooth from aboA'e 

 (A), and in transverse section 

 (B), nat. size. Carboniferous 

 Limestone ; Armagh. 



Family 3. Petalodontidae. Newberry and Wortlien. 



Teeth antero-posteriorly compressed, transversely elongated, arranged 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 mth 

 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 



