Among the Fishes of Old Red Sandstone, the _Coccosteus_ (Fig. 31, No. 1) was only partially cased in a defensive armour; the upper part of the body down to the fins was defended by scales. _Pterichthys_ (No. 2), a strange form, with a very small head, furnished with two powerful paddles, or arms, like wings, and a mouth placed far behind the nose, was entirely covered with scales. The _Cephalaspis_ (No. 3), which has a considerable outward resemblance to some fishes of the present time, was nevertheless mail-clad, only on the anterior part of the body. Other fishes were provided with no such cuirass, properly so called, but were protected by strong resisting scales, enveloping the whole body. Such were the _Acanthodes_ (1), the _Climatius_ (2), and the _Diplacanthus_ (3), represented in Fig. 32. [Illustration: Fig. 32.--Fishes of the Devonian epoch. 1. Acanthodes. 2. Climatius. 3. Diplacanthus.] Among the organic beings of the Devonian rocks we find worm-like animals, such as the _Annelides_, protected by an external shell, and which at the present day are probably represented by the _Serpulæ_. Among Crustaceans the _Trilobites_ are still somewhat numerous, especially in the middle rocks of the period. We also find there many different groups of Mollusca, of which the _Brachiopoda_ form more than one-half. We may say of this period that it is the reign of Brachiopoda; in it they assumed extraordinary forms, and the number of their species was very great. Among the most curious we may instance the enormous _Stringocephalus Burtini_, _Davidsonia Verneuilli_, _Uncites gryphus_, and _Calceola Sandalina_, shells of singular and fantastic shape, differing entirely from all known forms. Amongst the most characteristic of these Mollusca, _Atrypa reticularis_ (Fig. 33) holds the first rank, with _Spirifera concentrica_, _Leptæna Murchisoni_, and _Productus subaculeatus_. Among the Cephalopoda we have _Clymenia Sedgwickii_ (Fig. 34), including the _Goniatites_, illustrating the Ammonites, which so distinctly characterise the Secondary epoch, but which were only foreshadowed in the Devonian period. [Illustration: Fig. 33.--Atrypa reticularis.] [Illustration: Fig. 34.--Clymenia Sedgwickii.] Among the Radiata of this epoch, the order Crinoidea are abundantly represented. We give as an example _Cupressocrinus crassus_ (Fig. 35). The Encrinites, under which name the whole of these animals are sometimes included, lived attached to rocky places and in deep water, as they now do in the Caribbean sea. The Encrinites, as we have seen, were represented during the Silurian period in a simple genus, _Hemicosmites_, but they greatly increased in numbers in the seas of the Devonian period. They diminish in numbers, as we retire from that geological age; until those forms, which were so numerous and varied in the earliest seas, are now only represented by two genera. [Illustration: Fig. 35.--Cupressocrinus crassus.]