DIPLAC AXTHIDiE. 
23 
B. Paired spines between pectoral and pelvic fins 
well developed. 
Anterior dorsal fin-spine not exceeding tlie 
posterior in length. Climatius (p. 28). 
Anterior dorsal fin-spine much, exceeding the 
posterior in length. Parexus (p. 33). 
e / _ I /. ~ pV., t jt 
’ 'Ml 
Genus DIPLACANTHUS, Agassiz. 
[Poiss. Boss. Y. G. B. 1844, pp. 34, 40.] 
Syn. J Rhadinacanthus, P. H. Traquair, Geol. Mag. [3] vol. v. 1888, p. 512. 
Body fusiform, probably not much laterally compressed. Teeth 
minute or absent; orbit with ring of four circumorbital dermal 
plates. Pectoral fins large, and a median pair of stout spines fixed 
between these to the basal pterygia; a pair of free spines situated 
ventrally between the pectoral and pelvic fins. 
The pectoral fins in this genus are somewhat difficult of interpre¬ 
tation, but the accompanying woodcut (fig. 3) seems to represent 
Pig. 3. 
Pectoral arch and fins of Diplacanthus striatus, Ag.— b, basal cartilage ; 
cl. clavicle; i.cl, infraclavicle; m, median spine; s, fin-spine. 
the arrangement of the spines and pectoral arch in the type species. 
As is usually the case in crushed specimens, the fin-spines are exhi¬ 
bited from the dorsal aspect, and the ascending limb of the pectoral 
arch is bent forwards and exposed from the inner side. The greater 
portion of the pectoral arch consists of a pair of vertically elongated 
elements (cl.), each having a straight rod-like axis, filled with cal cite 
in the fossil, and thus originally either hollow or occupied by uncal¬ 
cified tissue; behind this axis there is a thin laminar expansion 
of bone, diminishing upwards, and apparently extending downwards 
and inwards to form an inferior limb. The pair of large bones does 
not mqet in the median line below, but is separated by a much 
smaller pair of bony laminae (i.cl.), united in a finely dentated 
