﻿tal;eoniscid.e. 425 



that further researches may lead to its dismemberment. The most 

 important contributions to present knowledge of the typical Palaeozoic 

 genera have hitherto been made by 11. H. Traquair 1 j and the ad- 

 ditional observations recorded in the following pages chiefly result 

 from the study of Mesozoic forms. 



Fig. 54. 



Palcsoniscus macropomus, Ag. — Head and pectoral arch, restored in outline, by 

 R. H. Traquair. 



a.f, anterior frontal ; a.g, angular ; br, branchiostegal rays ; cl, clavicle ; d, 

 dentary; e, ethmoid ; /, frontal ; i.cl, infraclavicle ; Lop, suboperculum ; 

 mx, maxilla ; n, narial opening ; op, operculum ; p, parietal ; p.cl, post- 

 clavicle ; p.op, preoperculutn ; p.t, post-temporal; pmx, premaxilla; 

 s.cl, supraclavicle ; s.o, circumorbital ring and suborbitals; s.t, supra- 

 temporal ; sq, squamosal. 



No 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 (a.f), 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. Palaeont Soc. 1877; Quart. Journ. Geol. Soc. vol. xxxiii. (1877) ; 

 and Trans. Roy. Soc. Edinb. vol. xxx. (1881, with plates in 1887). The Pahe- 

 ontographical Society's Monograph appears to have been abandoned, and has 

 been replaced in recent years by numerous desultory notes without figures. 



