RIIADINICHTHYS CARINATUS. 131 



denticulations are continued forwards for some distance over the surface as little grooves 

 — the scales inunediatclj bel)ind the shoulder, along the middle of the back as far as the 

 dorsal fin, and along the middle line of the belly as far as the ventrals, being also 

 sometimes more or less striated. The paired fins are sn)all, the median fins rather large, 

 and the caudal body-prolongation weak. 



Description. — The general form is slender, though, owing to post-mortem chdiWge^, the 

 exact proportions vary constantly in different individuals, as may be seen on comparing 

 the two specimens represented in PI. XXIX, figs. 1 and 2 ; on the whole, however, the 

 length of the head seems to be contained a little over five times in the total, and to be 

 equal to the greatest depth of the body at the ventral fins. The bones of the cranial shield 

 are ornamented with sharp delicate wavy ridges or strise. A specimen in my collection 

 shows most clearly the presence of extensive ossification in the periotic and alisphenoid 

 region of the cranium, and, moreover, a cast of the posterior semicircular canal of 

 the ear is most distinctly and beautifully preserved. The external ornament of the 

 facial bones consists, like that of the cranial shield, of delicate wavy ridges. The paired 

 fins are small ; there is, in the case of the pectorals, sufficient evidence (fig. 3) that the 

 principal rays were unarticulated till towards their terminations ; the ventrals, seldom 

 seen, are placed halfway between the pectorals and the anal. The median fins may be 

 considered rather large in proportion to the size of the fish. The anal commences 

 rather in front of a point equidistant between the origin of the ventrals and that of the 

 lower lobe of the caudal ; it is high and acuminate in front, with its posterior 

 border rather concave. The dorsal is similar in shape to the anal and commences only 

 slightly in front of the origin of the latter. The caudal is deeply cleft; the lower lobe 

 well developed ; but, as in the previously described species, the prolongation of the 

 body-axis along the upper lobe is comparatively delicate. The rays of all these fins are 

 slender, with distant articulations, their exposed surfaces being ganoid and smooth ; 

 the fulcra along the anterior margins of the fins are obvious though minute. 



The scales are rather large and quadrate on the flanks, but towards the median 

 ventral line they become low and narrow. A typical flank-scale, magnified, is 

 represented in PI. XXIX, fig. 5, and shows a brilliantly polished ganoid surface with 

 some scattered punctures, and along the posterior margin some seven to eleven sharp 

 denticulations. In some specimens, however, a certain amount of striation is produced 

 (fig. G) by the notches between the denticles being produced forwards for a little way 

 over the surface; in some examples, indeed, this striation is found over all the scales of 

 the anterior part of the flank. In every case, however, the scales of the nape of the 

 neck (fig. 4) seem to be striated all over, and a certain amount of striation is also 

 frequently observed on the narrow scales along the ventral margin between the 

 pectoral and ventral fins. 



Observations. — The type specimen of '^ Palceoniscus'" carinatus^ collected by Lord 

 Greenock, and described and figured by Agassiz, is now in the Royal Scottish Museum, 

 19 



