4 ON THE OCCURRENCE OF THE GENUS BELONOSTOMUS IN THE 



elongated laminae, ^-shaped in transverse section. To each arch is affixed a close 

 series of long, slender, compressed appendages, only superficially calcified, and 

 apparently to be interpreted as supports of the gill-filaments. 



(c.) Axial Skeleton of the Trunk. — The vertebral centre (Figs. 2 and 3) are well 

 ossified throughout, and the slender neural and haemal arches, with their spines seem 

 to be fused to them. They are deeper than long, and so far as can be determined 

 from imj)ressions of the terminal concavities (Fig. 3), the notochord was completely 

 constricted, no central perforation of the bone being distinguishable. A secondary 

 development of longitudinally-fibrous bone completely surrounds the primitive 

 double-cone of each centrum externally, and imparts to the vertebra the robust 

 appearance well shown in Fig. 2. 



{d.) Appendicular Skeleton. — Of the fins, only fragmentary remains of the 

 pectoral and caudal are preserved in the large fossil (Fig. 1). The rays are all robust, 

 laterally compressed, undivided for some distance proximally, but soon branching 

 and marked by numerous articulations. Of the supporting elements, nothing can be 

 discerned, and even of the membrane bones accompanying the pectoral arch there 

 remains little evidence. It is clear from the small fossil, M. 28, that there was a 

 pair of large supra-temporal bones externally ornamented with tubercles fused into 

 radiating and somewhat reticulating rugae. The same specimen also exhibits a small, 

 triangular, supraclavicle, adjoining the truncated postero-superior angle of the 

 operculum, and ornamented with tubercles of irregular size, partly fused into 

 concentric lines. Of the clavicle and pectoral arch itself, however, there are no 

 fragments sufficiently worthy of note. 



(e.) Squamation. — As usual in Belonostomus one series of flank scales is 

 excessively deepened, these being abruptly truncated below, but slightly rounded 

 and reflexed forwards at the upper extremity. A restoration of one example 

 from the anterior abdominal region is given, of the natural size, in Fig. 4. This 

 scale is about five times as deep as broad, crossed at its flexure by the lateral line ; 

 and the overlapped portion is relatively narrow. Immediately posterior to the 

 hinder margin of the overlapping scale is an area of nearly smooth ganoine, bounded 

 by a nodose longitudinal ridge. A jjarallel and more prominent longitudinal ridge, 

 separated from this, and from the hinder area by a furrow, divides the scale into two 

 nearly equal halves, and the posterior half is much ornamented. This ornament 

 consists first of large irregular tubercles, passing behind into small, nearly parallel, 

 though sometimes bifurcating transvere ridges, at right angles to the posterior 

 border. The scale immediately below the principal flank series is much deeper than 

 broad, and then follow about four small ventral scales, equally broad, but their depth 

 not exceeding half their breadth. One of the latter is shown, somewhat restored, in 

 Fig. 5; its overlapped superior border, with the large articular spine, is conspicuous, 



