134 GANOID FISHES OF THE CARBONIFEROUS FORMATION. 



head being rather greater than the depth of the body at the ventral fins, and contained 

 about four and a half times in the total. 



The cranial loof-boiics are ornamented with closely set, well-defined elevated ridges, 

 which, although wavy and soujcwhat contorted, mainly follow a longitudinal direction, 

 especially on the parietal and frontal plates and the posterior part of the superethmoidal ; 

 they are often bifurcated, intercalated and interrupted, and on the lateral parts of the 

 cranial shield these interruptions often become so frequent as to cause the ornament to 

 assume a somewhat tubercular character, which in some cases invades even the more 

 central parts. On the anterior part of the superethmoidal, which forms the usual pro- 

 jection over the mouth, the ridges are disposed transversely. 



The direction of the suspensonuni is very oblique, and the gape consequently wide. 

 The opercular bones are well developed and of the usual shape in this genus, but their 

 external markings are not distinctly preserved. The maxilla has its broad portion 

 ornamented with fine ridges, which run parallel with its superior and posterior margins ; 

 its infra-orbital process is tuberculated, and the tubercles are continued backwards as a 

 narrow band along the entire inferior or dentary margin of the bone. The beautifully 

 tapering mandible is covered externally with fine ridges which pass forward from the 

 angle in a somewhat radiating manner, so that below they are pretty parallel with the 

 inferior margin, while above they cut the suj)erior one at low angles. In large specimens 

 these ridges break up into minute tuberculation along the superior margin of the jaw 

 — a condition rarely met with in the smaller examples. The orbit is anteriorly placed, 

 and furnished with the usual arrangement of suborbital and circumorbital plates. 



The bones of the shoulder-girdle are ornamented with well-defined sub-parallel 

 ridges, which are arranged according to the common pattern, namely somewhat concen- 

 trically, and more or less parallel with the margins of the bones. 



The scales are of moderate size with narrow covered area, rhomboidal in shape and 

 increasing in obliquity, and diminishing in size towards the tail. On the flank they are 

 tolerably equilateral, but along the belly between the pectoral fins and the |)osteri()r part 

 of the base of the anal they suddenly become very low and narrow, their height 

 diminishing to one-half or one-third of their length. This change of form usually occurs 

 at the fourth or fifth scale downwards from the later;d line. A few large scales are seen 

 in front of the dorsal, anal, and lower lobe of the caudal fin, while on the body- 

 ])rolongation in the upper lobe of the latter the usual modifications of shape occur. 



As regards the scale-markings, their general plan may be described as follows : 

 Taking a scale from the anterior part of the flank (PI. XXX, figs. 2, 3), a few delicate 

 grooves are seen passing down along the anterior margin of the ganoid area, and then at 

 the antero-inferior angle, turning round so as to become parallel with the inferior 

 margin. The rest of the area presents, according to the size of the sj)ecimen, from four 

 to seven longitudinal elevations or feeble ridges running across the scale with a slight 

 downward obliquity as well as a slight tendency to radiation, and ending on as many 



