A treatise on zoology . quair, from A. S. Woodward, Proc. Geo!. Assoc.) , anterior dorso-lateral; ag,angular ; , anterior median dorsal; , anterior ventro-lateral; c, central; iha, dorsalanconeal; , dorsal articular; , extra-lateral; , external marginal; , internalmarginal; I, lateral; , lateral occipital; m, median ; m, in, in, in, marginals ; , medianoccipital; , median ventral; mx, maxilla ; o, ocular ; , posterior dorso-lateral; jnn, pre-median ; , posterior median dorsal; ptm, postmediaii ; , posterior ventro-lateral; si,semilunar;
A treatise on zoology . quair, from A. S. Woodward, Proc. Geo!. Assoc.) , anterior dorso-lateral; ag,angular ; , anterior median dorsal; , anterior ventro-lateral; c, central; iha, dorsalanconeal; , dorsal articular; , extra-lateral; , external marginal; , internalmarginal; I, lateral; , lateral occipital; m, median ; m, in, in, in, marginals ; , medianoccipital; , median ventral; mx, maxilla ; o, ocular ; , posterior dorso-lateral; jnn, pre-median ; , posterior median dorsal; ptm, postmediaii ; , posterior ventro-lateral; si,semilunar; t, terminal; , ventral anconeal; , ventral articular. Dotted lines indicatethe course of lateral-line canals. PTERICHTH YOMORrin 209 Cephalaspidomorphi. Especially iiuportant is the position andstructure of the orbits—so peculiar amongst Pisces, and so essentiallysimilar in both cases. The pectoral appendages may, moreover,be compared with tlie paired flaps of (Jephahi^pu^ also covered withdermal armoui-. ? Bothriulojiis ; lestoriMl. (Afler Patten.) r, cephalic shield ; cj\ ventral lobe of caudal fin ;cs, dorsal lobe of caudal tin ; (/../, seconci iloisal fin ; e, eye ; m, mouth ; p, i)ectoral jointedappendage ; sfil, fold uf skin (pelvic fjn ); /..-?, thoracic shield. Family Asterolepid.\e. A^erolcpu, Eich. ; Itenchthijs, Ag. ; Micro-brachins, Traq. ; Devonian, Eiuope. Bothriolepis, Eich. ; Devonian, Europeand Canada. 14 Sub-Grade 3. OSTEICHTHYES. The remainder of the true fish are included in this important characters distinguish them from the Chondrich-thyes, which remain at a lower grade of organisation. The cartila-ginous endoskeleton becomes to a considerable extent reduced inthe adult, and replaced by true bone, or some bone-like tissuederived from true bone (p. 355). The exoskeleton is also modified and strengthened by thedevelopment of bony tissues. AVhilst the primitive placoid scales(denticles) may remain, at all events in certain regions,
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