RETROSPECT OF PALEOZOIC AGE. 



beds of mountain limestone or conglomerates are formed of shells 

 of Brachiopods, such as spirifers, leptsense, &c. 



304. The Crustacea and Insects of the Carboniferous period 

 have been less accurately ascertained than the other divisions of 

 the animal kingdom. A few species of the fluviatile crustaceans, 

 the Cyprides, are found in the coal deposits. Small crustaceans 

 are also found in the iron-stone, which are referable to the 

 limulus or king-crab, a genus which abounds in the seas of India 

 and America. Dr. Mantell found in the iron-stone of Colebrook 

 Dale several fossil beetles resembling the curculio or diamond 

 beetle ; he also discovered the wing of a large neuropterous insect 

 closely resembling a species of the living Corydalis of Carolina. 



305. With the insects imbedded in the coal strata are found the 

 remains of those animals, to which they served as food. The fossil 

 scorpion (fig. 143) already mentioned is an example of this. This- 

 fossil, which measures about two and a half inches in length, is 

 embedded in coal-shale, with leaves and fruit; the legs, claws, 

 jaws and teeth, skin, hair, and even a portion of the trachea, or 

 breathing apparatus, are severally preserved. It had twelve- 

 eyes, the sockets of which remain. One of the small eyes and 

 the left large eye retain their forms, and have the cornea or 

 outer skin preserved in a corrugated or shrivelled state. The 

 hairy covering of the animal is also preserved, being neither car- 

 bonised nor decomposed ; the substance of which it consists, 

 electrine, has resisted decomposition and mineralisation . 



306. Among the fishes which lived during the Carboniferous 

 period, and which, as already stated, are exclusively of the 

 Placoid and Ganoid families, some genera are worthy of note. 



Of the Sauroid fishes, two genera, one called the Megalichthys, 

 is covered with enamelled smooth quadrangular scales, very 

 thick, and nearly an inch wide. The head is protected by strong 

 armour of enamelled plates. The teeth are large striated hollow 

 cones. This fish was from three to four feet in length. 



Another called the Holoptychius, attained in some instances the 

 length of thirty feet. The scales were thin and circular, varying 

 from one to five inches in diameter. The head is surrounded 

 with a sort of shagreen helmet, having a surface irregularly 

 ridged. It has large teeth of great density, some conical and 

 others long and slender. 



307. M. Agassiz has discovered about a hundred species of fossil 

 fishes of the Devonian and third Palaeozoic period, of which the 

 most remarkable are the Cephalaspis, Pterichthys, and Coccosteus. 



The Cephalaspis a Greek compound, signifying buckler-head 

 received its name from the head being protected by a buckler or 

 shield. The plates which cover it are united in a single osseous 



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