OPHIOPSIS. 75 



suboperculura is nearly three times as wide as deep, with an ascending process in 

 front. The uppermost branchiostegal ray is relatively large, and the others arc- 

 also stout. There seems to have been a large gular plate, but its presence is not 

 quite certain. 



In the axial skeleton of the trunk complete vertebral rings, about as long as 

 deep, occur throughout ; in the abdominal region the ribs are short and slender 

 (B.M. no. P. 9107 c). 



Behind the supratemporal bones, a pair of relatively large post-temporals is 

 seen (PI. XVI, fig. 4i,pU.). The supraclavicle is also large (PI. XVI, fig. 8), about 

 three times as deep as wide, with its exposed surface ornamented by ganoine partly 

 disposed in irregular oblique ridges. The clavicle is wide and much arched, and 

 similarly ornamented on its small exposed portion (B. M. no. P. 9436). The large 

 upper postclavicular scale is shown in the type specimen (PI. XVI, fig. 3). Fulcra 

 have been seen on the pelvic fins (B. M. no. P. 9107 c), and there seein to be traces 

 of them on the pectorals in the type specimen. 



All the scales are smooth, and those of the abdominal region, besides many of 

 the caudal region, are conspicuously though finely serrated. The principal scales 

 of the abdominal flank are about as broad as deep, with gently curved upper and 

 lower margins, and often marked with a few faint zig-zag lines parallel with the 

 posterior serrations (PL XVI, fig. 9). They are united by a large peg-and-socket 

 articulation (fig. 10), which becomes feeble or absent on the dorsal and ventral 

 scales and in the hinder half of the caudal region. The dorsal scales are much 

 broader than deep, with a tendency to the rounding of the postero-superior angle 

 (fig. 12). The ventral scales are also broader than deep (fig. 11), those in the 

 anterior half of the abdominal region excessively so. Ovate ridge-scales occur on 

 the caudal pedicle, but they are scarcely enlarged. 



Horizon ami Locality. — Lower Purbeck Beds: Vale of W ardour, Wiltshire. 



3. Ophiopsis dorsalis, Agassiz. Plate XVI, fig. 13. 



1844. Ophiopsis dorsalis, L. Agassiz, Poiss. Foss., vol. ii, pt. i, p. 291, pi. xxxvi, fig. 5. 

 1895. „ „ A. S. Woodward, Catal. Foss. Fishes B. M., pt, iii, p. 171. 



Type. — Nearly complete fish ; British Museum. 



Specific Characters. — A much elongated species about 16 cm. in length. Head 

 with opercular apparatus occupying one-fifth of the total length of the fish ; 

 maximum depth of trunk twice as great as depth of caudal pedicle, and contained 

 somewhat more than six times in the total length. External head-bones coarsely 

 tuberculated or rugose. Dorsal fin occupying greater part of back, .with about 

 35 rays, of which the longest do not equal the depth of the trunk at their point 

 of insertion ; pelvic fins in advance of the middle point between the pectorals and 



