ASPIDORHYNCHUS. 99 



Traces of short slender ribs occur both in the type specimen and in the original of 

 PL XX, fig. - ; and the other vertebral arches are also evidently delicate. 



Of the pectoral arch only the clavicle has been clearly observed. This bone 

 (PL XX, fig. 2, c/.) is much arched, with the upper and lower limbs about equal in 

 length, but the lower the wider. Its exposed portion is very narrow, smooth only 

 at its hinder margin, conspicuously marked by fine longitudinal ridges anteriorly. 

 The hinder border is slightly notched at the insertion of the pectoral fin, where 

 there are traces of a well-ossified scapula or coracoid. There appear to be no 

 specially modified post-clavicular scales. The pectoral fin (pet.), of which only the 

 base is known, comprises at least 10 smooth rays, of which most are very broad 

 and deeply overlapping. The position of the small pelvic fins is indicated in the 

 type specimen (PL XX, fig. 1, plo.) ; but it can only be stated that their rays are 

 smooth and broad, with distant articulations at the distal end. The dorsal (//.) and 

 caudal fins are known only by fragments in the same specimen ; but the anal fin 

 (a.) is better preserved, exhibiting at least 20 rays, of which the length of the 

 foremost is nearly equal to the depth of the tail at its insertion. The anal fin-rays 

 are smooth, divided, and distantly articulated in their distal half, and apparently 

 less crowded than the rays of the paired fins. The foremost ray seems to bear 

 traces of a fringe of minute fulcra. 



The total number of transverse series of scales in the type specimen seems to 

 have been slightly more than seventy, and they are seen to be arranged as in the 

 typical species of Aspidorhynchus from the Lithographic Stone of Bavaria. Those 

 of the abdominal region are best displayed in outer view in a fragment of which 

 part is represented in PL XX, fig. 3. All the scales are deeply overlapping, and their 

 hinder border is not serrated though sometimes slightly wavy. The rhombic dorsal 

 scales throughout the trunk (PL XX, figs, lb, 4) are covered with conspicuous 

 smooth ridges, variously wavy and sometimes bifurcating, which run diagonally. 

 The other scales, though also well enamelled, are only faintly and finely rugose. 

 In each transverse series of the abdominal region there are two of the ornamented 

 rhombic scales at the upper end, and there seems to have been a similarly orna- 

 mented median dorsal ridge-scale. The two principal scales of the flank are about 

 equal in depth, and the upper of these is crossed near its forwardly curved upper 

 end by the slime-canal, which notches the hinder border and occasionally opens by 

 a pore on the middle of the scale. The next lower scale is almost square, less than 

 half as deep as the principal flank-scales. Six, sometimes seven, very narrow 

 scales complete the series below, the lowest being a sharp-edged ridge-scale with- 

 out any serration. In the caudal region the flank-scales gradually become less 

 deepened, until on the caudal pedicle they are rhombic and nearly uniform in size. 

 There appear to be no enlarged ridge-scales. When exposed from within (PL XX, 

 figs. 1,2), all the scales of the abdominal region are shown to be united by a very 



