PALiEONISClDiE. 
425 
that further researches may lead to its dismemberment. The most 
important contributions to present knowledge of the typical Palteozoic 
genera have hitherto been made by R. H. Traquair 1 ; and the ad¬ 
ditional observations recorded in the following pages chiefly result 
from the study of Mesozoic forms. 
Tig. 54. 
PalcBoniscus macropomus, Ag. —Head and pectoral arch, restored in outline, by 
R. H. Traquair. 
ci.f, anterior frontal ; a.g, angular ; hr, branchiostegal rays ; cl, clavicle ; d, 
dentary; e, ethmoid ; f frontal; i.cl, infraclavicle ; Lop, suboperculum; 
mx, maxilla ; n, narial opening; op, operculum ; p, parietal; p.cl, post¬ 
clavicle ; p.op, preoperculum; p.t, post-temporal; pmx, premaxilla ; 
s.cl, supraclavicle; s.o, circumoi'bital ring and suborbitals; s.t, supra- 
temporal; sq, squamosal. 
Ho precise particulars are forthcoming as to the ossifications in 
the chondrocranium, but the dermal or membrane-bones of the head 
are conspicuous and well-known. The cranial roof is provided with 
a continuous shield, of which a small pair of parietals (fig. 54, p) 
and the flanking squamosal plates (sq) form the hinder portion, while 
a large pair of elongated frontals (/), with or without a separate pair 
of lateral plates, constitutes the middle portion ; a large, azygous eth¬ 
moidal or rostral plate ( e) completes the shield anteriorly, is flanked 
on each side by a so-called anterior frontal element («./), and with 
the latter surrounds the pair of narial openings (n). The base of 
the cranium also has the ordinary, well-developed parasphenoid 
membrane-bone. The jaws and cheek are likewise covered with 
1 Monogr. Palseont Soc. 1877; Quart. Journ. Geol. Soc. vol. xxxiii. (1877); 
and Trans. Roy. Soc. Edinb. vol. xxx. (1881, with plates in 1887). The Pala- 
ontographical Society’s Monograph appears to have been abandoned, and has 
been replaced in recent years by numerous desultory notes without figures. 
