Family V Paleoniscide

FAMILY V PALEONISCIDE.

The Placoganoids, so richly represented in the Devonian epoch, disappear in the carboniferous one ; the Lepidoganoids increase in number. In the present family they combine with rhomboid scales, a heterocercal tail, and jaws armed with numerous, minute, close-set, rather blunt teeth. The type genus is Palceoniscus (fig. 51), species of which range through out the carboniferous and Permian beds : it is characterized by moderate-sized fins, the dorsal, D, being single, and opposite the interval between the anal, A, and ventral, V, fins : each fin has an anterior spine ; the fore-part of the head is obtuse.

Palooniscue

(Permian).

In the Pakeonisci from the coal formations at Burdie House, near Edinburgh, the outer surface of the scales is striate and punctate,- e.g., in P. ornatissimus, P. striates; but in the Pakeonisci of other British localities, and of the continental and American coal formations, the scales are smooth, e.g., in P. fultus, from North America, P. Duvernoyi and P. minutes, from the coal beds of Munster AppeL In the Palceonisci from the Permian copper schales and zechstein, the scales are striate or punctate : the Palceoniscus Freieslebeni is the most common in these beds, and was the first recognized species of the genus. Of

this there are now forty known species, chiefly from carboniferous and Permian eras : one from the Keuper beds at Rowington, Warwickshire, appears to be the last representative of the genus : it is the Palceoniscus "verges of Egerton.

Amblypterus,

with a geological range like that of Pak:vont:sous, differs in its shorter and deeper tail, and larger body-fins, which are devoid of anterior spines. In fig. 52, a indi cates the outer surface of parts of two series of the rhomboidal ganoid scales ; and b the inner surface of two scales, showing the ridge produced at one end into a projecting peg, which fits into a notch of the next scale, in the way that tiles are pegged together in the roof of a house. The species affording the above structure is the Amblypterus striatus from the coal formations at Newhaven.

Several species of Amblypterus have left their remains in the muschelkalk, at which triassic period the genus seems to have passed away.