. The testimony of the rocks; . o both orders; and among the extremer forms, in whichPalaeontologists for a time failed to detect that of the fishat all, we reckon those of the genera Coccosteus, Pterich-thys, and Cephalaspis. The more aberrant genera, however,even while they consisted each of several species, werecomparatively short lived. The Coccosteus and Cephalaspiswere restricted to but one formation apiece; while thePterichthys, which appears for the first time in the lowerdeposits of the Old Red Sandstone, becomes extinct at itsclose. On the other hand, some of the genera that exem-pli
. The testimony of the rocks; . o both orders; and among the extremer forms, in whichPalaeontologists for a time failed to detect that of the fishat all, we reckon those of the genera Coccosteus, Pterich-thys, and Cephalaspis. The more aberrant genera, however,even while they consisted each of several species, werecomparatively short lived. The Coccosteus and Cephalaspiswere restricted to but one formation apiece; while thePterichthys, which appears for the first time in the lowerdeposits of the Old Red Sandstone, becomes extinct at itsclose. On the other hand, some of the genera that exem-plified the general type of their class were extremely longUved. The Celacanths were reproduced in many variousspecies, from the times of the Lower Old Red Sandstone tothose of the Chalk; and the Cestracions, which appear inthe Upper Ludlow Rocks as the oldest of fishes, continue9 98 THE PAL^ONTOLOGICAL in at least one species to exist still. It would almost seemas if some such law influenced the destiny of genera in this Fig. PTERICHTHTS OBLONGUS.(One half nat. size.) ichthyic class, as that which we find so often exemplified inour species. The dwarf, or giant, or deformed person, isseldom a long hver;—all the more remarkable instances oflongevity have been furnished by individuals cast in theordinary mould and proportions of the species, l^ot a fewof these primordial ganoids were, however, of the highestrank and standing ever exemplified by their class; and wefind Agassiz boldly assigning a reason for their superiorityto their successors, important for the fact which it embodies,and worthy, as coming from him, of our most respectfulattention. It is plain, we find him saying, that before HISTORY OF ANIMALS. 99 the class of reptiles was introduced upon our globe, thefishes, being then the only representatives of the type ofvertebrata, were invested Avith the characters of a higherorder, embodying, as it were, a prospective view of a higherdevelopment in another class, which
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