A. Smith Woodward — Eocene Sihiroid Fishes. 305 



But the British Museum does not appear to possess any example 

 sufficiently large to have pertained to a fish of the dimensions 

 indicated by the pectoral arch No. 25612 ; and the fossil figured by 

 Dixon (No. 25735a) is one of the finest and best preserved. The 

 spine is remarkably straight, neither the anterior nor the posterior 

 border exhibiting more than the slightest curvature, and the distal 

 tapering is but gradual. The lower end shows the usual facettes 

 for its connection with the interspinous bones, and there is the 

 ordinary " shackle joint." The row of denticles upon the anterior 

 edge is prominent in unabraded specimens, and they are largest in 

 the middle, diminishing towards either extremity ; those at the 

 base are merely minute tubercles, but those still higher are well- 

 defined booklets, with the points at first directed upwards and 

 finally downwards. 



The short blunt spine, with bifurcating base, situated in front of 

 the larger weapon, and serving as a kind of " bolt " or fulcrum, 

 has also been met with at Bracklesham, and is shown of the natural 

 size in Fig. 1. There are likewise some fragments of the modified 

 interspinous bones, though these exhibit no special features of 

 interest. 



Cranial Bones. — But the most satisfactory materials for discussion 

 consist in a number of fragments of the cranium, which were long 

 ago labelled by Sir Philip Egerton and Mr. William Davies as 

 pertaining to the present species, though no description of them 

 seems to have been hitherto published. These bones are ornamented 

 externally in a very similar manner to the clavicular plate already 

 noted, and their size is such that they may well have belonged to 

 the fishes indicated by the detached fin-spines. The only element, 

 however, that is capable of certain determination, is the supra- 

 occipital bone — fortunately one of the most characteristic bones in 

 the Siluroid skull — and of this four good examples are preserved : 

 the finest is shown of the natural size, viewed from above, in 

 Fig. 2. Anteriorly, there is a small median process dividing the 

 posterior ends of the frontals ; on either side, the sutural connections 

 with the successive laterally-placed bones are more or less dis- 

 tinguishable, and the greatest breadth is attained between the 

 squamosals ; and posteriorly, where the lateral borders are free, 

 the element exhibits scarcely any tapering, and has a comparatively 

 abrupt termination. The upper surface is raised into a median 

 longitudinal keel in the hinder half of the bone, and from the 

 anterior extremity of this there diverge two well-marked mucus- 

 canals, which appear to extend towards the point of junction of 

 the frontal and postfrontal on each side. On the inferior aspect, 

 the most noteworthy feature is the strength of the septum between 

 the lateral muscles, below the post-cranial extension of the bone. 

 There is no trace of a supraoccipital fontanelle. 



Systematic Position. — From the foregoing facts, it is obvious, that 

 the Siluroid species under consideration was characterized (i.) by the 

 presence of a strong dorsal fin-spine in addition to the pectorals ; 

 (ii.) by a large, ornamented dermal plate attached to the scapular 



DECADB in. VOL. lY. NO. VII. 20 



