616 GANOIDS abdomen and ribbed and groined arch of the back add to the strength of the armature with- out increasing the weight the creature re- sembling a " subaqueous boat, mounted on two oars and a scull;" and this strange fish is a characteristic organism of the old red sand- stone. The genus coccosteus has not the pec- toral appendages of the preceding animal, and the head and anterior part only of the trunk are covered with a bony helmet and cuirass, the caudal portion being naked; it has one dorsal and one anal fin ; the mouth is furnished Coccosteus. with small, equal, conical teeth. The most remarkable peculiarity in this fish, unique among vertebrated animals as far as known, is that the jaws possessed both the usual vertical motion, and also a horizontal movement as in crustaceans, indicated by the two sets of teeth, one on the upper edge of the jaw and the other on the line of the symphysis, the latter of which, if brought into action at all, could only be so by the lateral movement of the jaws. The jaws of coccosteus are als,o interesting, as presenting the most ancient internal bone which has displayed its structure under the micro- scope. The jaw of this ancient fish shows the Haversian canals, the lacunae and osseous cells, as in the bones of man at the present time ; showing the extension of the same plan through the most distant ages, and by a fair inference to the beginning of vertebrate existence. The genus cephalaspis, or buckler-head, had a thin triangular body, and crescent-shaped head cov- ered with a singular shield-like plate, with later- al prolongations extending along the sides ; body covered by vertical rows of scales ; no ventrals nor pectorals, and two dorsals. It lived at the same time with large placoids, armed with dor- sal spines (of which the spines only remain), Cephakspis. and with a gigantic lobster-like crustacean more than 4 ft. long ; it belongs to the middle por- tion of the old red sandstone. The family of sauroids, of which the gar pike is one of the few living representatives, had pointed conical teeth alternating with small brush-like ones ; the skeleton bony; the scales flat, rhomboidal, and completely covering the body ; those living before the Jurassic age had unequal-lobed tails, while the homocercal genera flourished at a more recent period. The genus megalichthys was a formidable fish of large size ; the scales of the body and the plates of the head had such a brilliant enamelled surface, "that they may still be occasionally seen in the shale of a coal pit, catching the rays of the sun, and reflecting them across the landscape, as is often done by bits of highly glazed earthenware or glass." The genus diplopterus was of smaller size, with an elongated tapering body, flat head, rounded muzzle, two dorsals, two anals, and the caudal fin truncated almost vertically, the lobes coming off laterally from a prolongation of the vertebral column ; their scales were of great brilliancy, and must have flashed brightly through the woods of the coal period, as they leaped into the air in sport or in pursuit of prey. The genus pygopterus had the fins greatly developed, and a heterocercal tail. AspidorJiynchus had a much elongated body, homocercal tail, the upper jaw prolonged into a beak and extending beyond' the lower ; the scales large. The former belongs to the coal and magnesian limestone formations, Aspidorhynchus. and the latter to the Jurassic. The coelacanth family is characterized by having all the fin rays and bones hollow, a peculiarity not found in other ganoids ; and all the fin rays are stiff, articulated only at their bases, and sup- ported on interapophysal small bones ; they occur in all the ages from the lower Devonian to the chalk formations, most numerous in the red sandstone and coal strata. In the genus asterolepis, one of the earliest- and largest of the ganoids, the bony plates of the head are ornamented with star-like markings, and the scales of the body are delicately carved ; Hugh Miller says its cranial bucklers have been found in the flag stones of Caithness, " large enough to cover the front skull of an elephant, and strong enough to have sent back a musket bul- let as if from a strong wall." It must have equalled in size the largest alligator, and its teeth throughout the jaw had the reptilian peculiari- ty of being received into deep pits opposite, causing them when the mouth is shut to lock like the serrations of a bear trap. The genus Jioloptychius was of very large size, with rough scales several inches in diameter, the cranial bones sculptured like those of the crocodile, and conical teeth larger than those of any liv- ing reptile. The H. (rhizodus) Hibberti, the largest of about 20 described species, was of such a giant size that the words applied in Job to leviathan might appropriately be given to it ; this reptilian fish must have been 40 ft. in length, with teeth three times larger than those of the largest crocodile, and covered with an impenetrable coat of mail. There were several smaller holoptychians in the red sandstone, even more strongly armed than this giant of the coal period. For further details
