SUB-CLASS I 



SELACHIl 



27 



Sub-Order C. ASTEROSPONDYLI. Hasse, 



Vertehral centra when completely formed amphicoelous, strengthened hy secondary 

 plates of calcißed tissue which radiale outwards from the excessively constricied 

 cylinder. Five gilt clefts on each side. Two dorsal fins and one anal fin 

 Lower Carboniferous to Recent. 



Fi(i. 4it. 



Orodxts ramosus, Ag. Carboniferous Limestone ; 

 Arinagh (after Davis). 1/2. 



Family 1. Oestraciontidae. Agassiz. 



Dorsal fins each armed with a spine. Teeth numerous, mostly obtuse, never fused 

 into continuous plates ; several series simultaneously in funäion. Radiating plates of 

 the vertehral centra few and short ; vertehral column not calcified in the earlier forms. 

 Lower Carboniferous to Recent. 



1^ This family is characteristic of the later Palaeozoic and the Mesozoic 



formations ; it is represented in existing seas solely by one genus, 



Cestracion. 



Orodus, Ag. (Fig. 49), kno wn only by obtuse elongated teeth. The dental 



crown raised in the middle, and its surface marked with more or less prominent 



wrinkles, which rise from each long margin 



or from a median longitudinal crest. Base 



of tooth very stout. 0. ramosus, Ag. (Fig. 



49), and other species from the Carboniferous 



Limestone of Britain, Belgium, and Russia. 



Also numerous species in corresponding 

 American formations. 



Campodus, Kon. (Agas- 

 sizodus, St. J. and W. ; Arpagodus, Traut.). Teeth almost 

 identical with Orodus, but distinguished by buttressed 

 condition of the outer border of the crown. Symphysial 

 series greatly enlarged, and fused. Carboniferous. Edestus, 

 Leidy ; Campyloprion, Eastm. ; and Helicoprion, Karp., 

 known only by their arched or coiled symphysial dentition. 

 Carboniferous and Permian. 



Tristychius, Ag. (Ptychacanthus, Ag.), (Fig. 50). Dorsal 

 fin spines with a few sha^-D longitudinal ridges distally, 

 three only — one upon the front margin and one on each 

 side — extending far downwards. Teeth probably as in 

 Sphenacanthus. T. arcuatus, Ag. Carboniferous. 



Sphenacanthus, Ag. Töeth rather high-crowned, with a 

 large principal cusp and smaller lateral cusps diminishing 

 in size outwards, more or less marked by superficial 

 wrinkles ; base depressed, forming a slight expansion back- 

 wards. Notochord persistent. Dorsal fin spines marked 



Ag^BZfedün.rh!f(Ä) ^^*^ robust lougitudinal ridges, in part nodose ; posterior 



shagreen-scaie (B), and denticles small and numerous, in two series, one upon each 



si?e. Lower"ca?boS! lateral margin of the flattened or slightly concave posterior 



stTck).' ^"""^^^"'^ ^^^^''' face. Few minute comb-shaped shagreen granules. S. 

 costellatus, Traquair sp., known by nearly complete fish 



from Calciferous Sandstones (Lower Carboniferous) of Eskdale, Dumfries. 



Fig. 50. 



