1 38 PALAEONTOLOGY 



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 Amhlyptcrus striatus from the coal- 

 formations at Newhaven. 



Several species of Amhlypt&rus have left their remains in 

 the muschelkalk, at which triassic period the genus seems to 

 have passed away. 



Family VI. — SAURiCHTHYiDyE. 



Magnificent species of heterocercal rhomb-scaled Ganoids, 

 with large dispersed laniary teeth, sometimes of a size rivalling 

 those of great Saurians, for which they have been mistaken, 

 have left their remains in the coal strata at Carluke, near 

 Glasgow, and other localities, and constitute the genus Mcga- 

 liclithys of Agassiz. The head is defended by strong ganoid 

 plates, of a beautiful polish ; the trunk-scales are usually 

 granulate exteriorly. In this genus, as in the type of the 

 family, the fulcra of the fin-rays are in two rows : all the 

 known species of Saurichthys are triassic. 



Pygopt&rus and Aerolepis, with fin-fulcra in a single row ; 

 Eurynotus, Elonichthys, Pledrolepis, Graptolepis, Orognathus, 

 Pododus, Acanthodcs, and Diplopt&rus, are carboniferous genera 

 of Ganoids, with rhomboid scales. Ccelacanthus, Isodus, Pltyl- 

 lolcpis, Hoplopygus, Uronemus, Colonodus, Centrodus, Asterolepis, 

 Psammostcus, and Ostcoplax, are genera of Ganoids with 

 rounded scales, represented by species in carboniferous strata. 



Of the above-named genera, Acrolepis, Pygopterus, Pakco- 

 niscus, and Ccelacanthus, continue to be represented in Permian 

 beds ; in which also are found species of the ganoid genera 

 Dorypterus, Holacanthodus, and Glofadodus, if the teeth on 

 which the latter is based be not those of Platysomus, a pycno- 

 dont genus which is both Permian and carboniferous. 



The formations of the mezozoic or secondary periods give 



