SUB-CLASs r 



SELACHI1 



27 



Sub-Order C. ASTEROSPONDYLI. Hasse. 



Vertebral centra when completely formed amphicoelous, strengthened by secondary 

 plate's of calcified tissue which radiate outwards from the excessively constricted 

 primitive cylinder. Fire gill clefts on each side. Two dorsal fins and our anal fin 

 present. Lower Carboniferous to Recent. 



Family 1. Oestraciontidae. 



Agassiz. 



A 



a, odus i amosu-s, Ag. Carboniferous Limestone ; 

 Armagh (after Davis). 1 /o. 



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

 into continuous' plates ; several series simultaneously in function. Radiating plates of 

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

 Lower Carboniferous to Recent. 



This family is characteristic of the later Palaeozoic and the Mesozoic 

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

 Cestracion. 



OroduSj Ag. (Fig. 49), known 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 \Y. ; 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 sharp 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. Teeth 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- 



Fig. 50. wards. Notochord persistent. Dorsal fin spines marked 



Tristychius arcuatus w j t h r0Dus t longitudinal ridges, fti part nodose; posterior 



shagreen-scale (/,'), and denticles small and numerous, m two series, one upon each 



(C Lo^Va;S',l! lateral margin of the flattened or slightly concave posterior 



c 





/; 



size. 



ferous 



Stock) 



Scotland (after 



s. 



face. Few minute comb-shaped shagreen granules. 

 costellafus, Traquair sp., known by nearly complete fish 

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



