218 Notes on Acanthodian Sharks 
striatus in the British Museum, P. 36,582, cf. P. 1757, a (Fig.19),which 
shows a distinct pelvic girdle, p. At the base of the fin spine the en- 
larged supporting mass, r-+ b, represents, we infer, the fused baso- 
radial elements. At d appears a pair of distinct plates, dermal appar- 
ently in origin. Whether they are related to the much discussed series 
of “fin spines passing between the pectoral and pelvic fins ” is not clear. 
Sense Organs.—Our knowledge of the end organs of Acanthodians ap- 
pears to be confined to a few notes on the lateral line and on the large 
eyes protected by “ four dermal plates.” As to the former structure, 
Smith Woodward remarks” that “a single lateral line occurs high on 
each flank, marked not by any tubular or other excavation of the scales, 
but by the ridge-like displacement of two series, between which the organ 
originally extended. The supposed evidence of additional sensory canals 
appears to the present writer to be due to a misinterpretation of the dis- 
placed dorsal and ventral ridges, which exhibit no median series of scales.” 
Reis, in this connection,” has made the interesting observation that the 
lateral lines are joined by an occipital commissure very much as in recent 
elasmobranchs and teleostomes; and he refers also to the presence of a 
median canal in the forehead which he compares to (or parallels with ?) 
the rostro-median canal of Chimera; he figures, finally, a supraorbital 
canal and refers to the absence of a suborbital branch arising from the 
main canal in that region. Reis’s figure representing these conditions ~ 
is of especial importance. ‘To the foregoing notes upon sensory struc- 
tures I may add: The “additional sensory canals,” in spite of the 
skeptical comment of Smith Woodward, are beautifully seen in several 
specimens in the British Museum and in the Edinburgh Collection. I 
refer particularly to Climatius grandis and Ischnacanthus gracilis” (Figs. 
30, 31, Edinburgh, and 32, this after No. 241, Powrie Collection). In 
these particular forms the branching of the lateral line, /1, in the 
neighborhood of the dorsal spine is, indeed, so common an occurrence 
that one might even maintain that it was the normal condition. It has 
not, however, been observed to occur on both sides in the same indi- 
vidual; nor is it definite that it occurs always on the same side, although 
a close examination has convinced me that it occurs on the right side in 
most cases. The most remarkably preserved sensory structures in 
Acanthodians are probably shown in the specimens of A. bronni (from 
20 Cat. Foss. Fishes, Vol. II, p. 5. 
21 Morph. Arb. Schwalbe, VI, pp. 195-196. 
2 Op. cit., p. 195. 
73 London, P. 6974. 
