378 RAMSAY H. TRAQUAIR ON THE 
vided with fulcra (certainly distichous in Hurynotus), their rays are ganoid 
externally, closely set, articulated throughout, and in the fore part of the fin 
their demi-rays imbricate from before backwards. 
The line of the top of the head slopes downwards and forwards at an angle, 
which in some forms (Platysomus) becomes very high, and usually shows a 
slight convexity or rounded angle above and in front of the orbit. The snout 
is pointed and prognathous, and the orbit and nasal openings tend to become 
more and more removed from it in an upward and backward direction. The 
cranial roof is covered with ganoid plates corresponding to those of the 
Paleoniscide. There are two parietals touching each other in the middle line, 
each of which is flanked by a squamosal (dermal-pterotic). Over the orbits 
are two frontals, and on each side a posterior frontal (dermal-sphenotic) forming 
the posterior-superior orbital margin, and an anterior frontal (lateral dermal- 
ethmoidal) forming its anterior-superior boundary. Between the anterior 
frontals is a medium superethmoidal, and the nasal openings are formed each 
by a rounded notch on the outer side of the superethmoidal, completed by a 
similar one on the opposed margin of the adjacent anterior frontal. The hyo- 
mandibular slopes downwards and usually also a little forwards; the osseous 
part of the palato-quadrate apparatus displays, in Cheirodus at least, three bony 
elements, pterygoid, mesopterygoid and quadrate, of which the pterygoid is by 
far the largest. ‘The mandible shows the presence of articular, dentary, angular, 
and splenial pieces, its external aspect being occupied almost entirely by the 
dentary. The maxilla is a more or less triangular Plate, the premaxilla is 
pointed and often beak-like. 
The opercular apparatus consists of an opercular plate, below which is an 
interopercular, often as large as, or even larger than the opercular, while the 
preoperculum placed in front of these covers the hyomandibular as well as also 
a portion of the cheek. The branchiostegal rays take the form of narrow 
imbricating plates, and where, as in Hurynotus and Cheirodus, afavourable view 
has been obtained, a median lozenge-shaped plate is seen connecting the right 
and left series behind the symphysis of the mandible. The orbit is bounded 
a. 
od 
= 
below and behind by a chain of suborbital plates, besides which there is evi- i 
dence of a narrow circumorbital ring passing round its entire circumference. 
The teeth vary very much in shape in different genera, but so far as yet 
observed never display the acutely conical form characteristic of the Paleeonis- 
cidee. They may be either tubercular or obtuse, with or without constricted 
neck or base, or cylindro-conical, with constricted base more or less marked. 
They are usually present upon the splenial and on the pterygoid, not always 
so upon the dentary of the mandible, the maxillary margin, or upon the 
premaxilla. ; 
The notochord is persistent, but the neural and hzmal arches and spines are 
