Lign. 202. Asterolepis. Devonian. (1/2 nat. size)
Inner side of portion of the lower jaw.
(After Miller.)
ASTEROLEPIS.
In Mr. H. Miller’s charming work just referred to we have a full and clear account of the singular fossil fish the Asterolepis. Remains of this gigantic Ganoid were first found in Russia.[554] Its name is derived from the stellate markings on the dermal plates of the head, which are of great size, and form a strong expanded buckler, the orbits of the eyes being situated near the anterior border. (See Miller’s Asterolepis, pp. 74, et seq. figs. 27-29.) [Lign. 202] shows a part of the lower jaw of this fish, seen on the inside. Along the upper margin are seen a "thickly set row of small broadly-based teeth,"—these are ordinary fish-teeth; and behind this edge-row of small teeth, b, there occur "a thinly set row of huge reptile-teeth, based on an interior platform of bone, which formed the top of the cartilage enclosing box composing the jaw." (Miller.) These large teeth, a a, are longitudinally striated, and generally bear two sharp lateral cutting edges.[555]
[554] Casts of the fossil bones from Russia are in the British Museum; Petrif. p. 435.
[555] The microscopic structure of both kinds of teeth is elegantly figured in Mr. Miller’s work, pp. 81, 82.
Macropoma Mantelli. Wond. p. 348. (Foss. South D. tab. xxxvii. xxxviii.; Petrif. p. 436, Lign. 89.)—This Cœlacanth fish is from one to two feet in length, of an elongated fusiform shape, with a large head and two dorsal fins; the anterior fin is imbedded, and has seven or eight strong spinous rays, the first two of which have numerous spines. The opercula are very long and large (hence its name); the scales[556] are garnished with adpressed spines, disposed in semicircular rows (see [Lign. 185], fig. 2). The teeth are small, conical, and numerous.
[556] See Prof. Williamson’s Memoir, Philos. Trans. 1849, p. 435; pl. xliii. figs. 27, 28.
Several specimens of this fish are almost perfect. The bones of the cranium, the jaws, teeth, opercula, branchial rays, palatine arches, the surface of the body covered with scales, all the fins, the pelvic bones, the vertebræ and their apophyses, all remain.
In one example, the vomer, covered with minute teeth, is exposed. But the most extraordinary fact relating to these Ichthyolites, is the preservation, in every specimen, of the air-bladder;[557] even its membranes remain, and separate in flakes; and the ramification of the minute vessels is visible under a high magnifying power. In some instances this bladder is displaced and much distended; but in general it occupies its natural position, and retains its elongated, sub-cylindrical form, with a few annular constrictions or folds.