44 



WEALDEN AND PURBECK FOSSIL FISHES. 



and its sheatli are two sectors of spongy bone (pi-) wliicli thicken upwards, until 

 they nearly surround the canal for the spinal cord and form the expanded base of 

 the neural arch {ii.a.). Two similar but larger sectors of spongy bone {hy.) encircle 

 the lower part of the notochordal space, each bearing a short transverse process or 

 parapophysis (t.) for the support of the rib. Each dorsal piece is directly con- 

 tinuous with the rod-shaped lamina of the neural arch, which is inclined backwards 

 and does not appear[to be fused with its fellow of the opposite side at the upper 

 end, where it is in contact with the long rod-shaped neural spine {n.s.), also inclined 

 backwards and curved so as to be a little concave anteriorly. The ribs are com- 



FiG. \H.- Lepxdotus manielli, Agassiz ; anterior vertebra m front view (A) aiul in transverse section (B), 

 nat. size.-Wealden : Hastings. Beckles Collection (B. M. no. P. (J34.8 c). hy., hypooentrum ; 

 n.a., neural ardi ; «..s., neural spine; p^-. pleurocentrum ; »-., rib; f., process on hvpoccntrum for 

 articulation of rib. 



paratively slender and extend considerably more than half-way towards the ventral 

 border of the fish. 



The supratemporal plates are small, and usually in four pairs, as shown in the 

 type specimen of L. fittoni (PL VIII, fig. 2 a, .v/.), and in the immature head 

 represented in PI. IX, d. Two, however, are sometimes fused together, so that 

 the series becomes unsymmetrical (PI. VIII, fig. 3). All are marked with a coarse 

 and irregular rugose ornament, with occasional indications of the traversing slime- 

 canal. Each of the inner pair of plates is wider than long, and extends along at 

 least half of the parietal border. The next two plates are much smaller, being 

 longer than wide, the inner plate in contact solely with the parietal, the outer plate 

 bordering an angle between the parietal and squamosal bones. The outermost 

 plate of the series, which is slightly larger than the two latter, bounds both the 



