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CATALOGUE 
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FOSSIL FISHES 
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Class PISCES. 
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Subclass I. ELASMOBRANCHII.^ -A 
Skeleton cartilaginous, membrane-bones absent (? except rarely, 
ill-defined). Mandibular suspensorium articulated with the cranium; 
gill-clefts separated, without external cover. Exoskeleton, when 
present, structurally identical with the teeth. In the living forms 
—optic nerves not decussating, bulbus arteriosus of the heart with 
three series of valves, intestine with a spiral valve, and ovaries with 
few large ova. 
Order I. ICHTHYOTOML 
Endoskeletal cartilage permeated throughout with granular calci¬ 
fications. Notochord rarely or never constricted; calcifications of 
the sheath arrested at the most primitive “ rhachitomous ” stage, 
except in the caudal region. Neural and haemal arches and spines 
long and slender ; no intercalary cartilages. Pectoral fins with long 
segmented axis (“ archipterygial ”). 
Family PLEURACANTHIDiE. 
Body slender, but slightly depressed; mouth terminal; tail diphy- 
cercal. Dorsal fin elongate, low, continuous along the back from a 
point shortly behind the head ; slender interneural cartilages more 
numerous than the neural spines. Pectoral fin with biserial arrange¬ 
ment of cartilaginous rays. 
B 
