[3] Description of Ceratodus. “Phil. Trans.,” 1871, ii.
[4] In the formula generally preceding the description of a fish, “L. lat. 40,” would express that the scales between the head and caudal fin are arranged in 40 transverse series; and probably, that the lateral line is composed of the same number of scales. “L. transv. 8/5” would express that there are eight longitudinal series of scales between the median line of the back and the lateral line, and five between the lateral line and the middle of the abdomen.
[5] Pterotic of Parker.
[6] C. Hasse has studied the modifications of the texture of the vertebræ and the structure of the Chondropterygian skeleton generally, and shown that they correspond in the main to the natural groups of the system, and, consequently, that they offer a valuable guide in the determination of fossil remains.
[7] The Ganoids formed at former epochs the largest and most important order of fishes, many of the fossil forms being known from very imperfect remains only. It is quite possible that not a few of the latter, in which nothing whatever of the (probably very soft) endoskeleton has been preserved, should have to be assigned to some other order lower in the scale of organisation than the Ganoids (for instance, the Cephalaspidæ).
[8] As first proposed by Huxley.
[9] Stannius (pp. 60, 65) doubts the pure origin of these two bones from membranous tissue, and is inclined to consider them as “the extreme end of the abortive axial system.”
[10] Parker’s nomenclature is adopted here.
[11] According to Langerhans “Untersuchungen über Petromyzon planeri” (Freiburg, 1873) an optic chiasma exists in that species.
[12] This nerve is not shown in the figure of the brain of the Perch (Fig. 41), as reproduced above from Cuvier.