133 
base, and magTiified 20 diameters, shows the internal part or 
core to be rather more than half the diameter of the spine, 
and apparently hollow. The bony structure surrounding 
this is composed of numerous ridges, without definite 
arrangment, between and amongst which are pits or vacuoles. 
The whole presents a Jabyrinthoid appearance. The bony 
part of the section has been cracked, both from the external 
and internal margin. The cracks are filled up with iron 
pyrites. 
HoPLONCHUs, gen. no v. 
Two or three spines from the Bone-bed present cha,racters 
difiering from any previously described, they are IJ inches 
long and -p^ broad at the base, they are sti-aight except a 
slight curve on the anterior margin towards the point. 
From the apex to a quarter of an inch from the base, the 
side of the spine is ornamented by longitudinal enamelled 
ridges, six in number ; the remaining portion has been 
imbedded in the tegument of the fish. The line dividing 
the two parts lies obliquely across the spine, the posterior 
border beino^ the shorter one. The rido-es in one or two 
instances run into each other, presenting a bifurcated 
appearance. The whole of the spine is slightly compressed. 
Along the posterior margin are a series of minute denticles, 
scarcely distinguishable without the aid of a magnify ing- 
glass. 
The two genera to which they are most nearly allied are 
Onchus and Homacanthus of Agassiz. It difi'ers from the 
former in having denticles, and from the latter in being 
straight and having the furrows or ridges homogeneous. 
Sir Philip Egerton, who has a specimen of the spine, 
suggests the generic name " Hoplonchus," as signifying the 
character distinsruishincr them from Onchus. 
