26 
ACANTHODII. 
43018. Specimen assigned to D. crassispinus by Agassiz, op. cit. 
pi. xiii. fig. 2 ; Orkney. Purchased , 1871. 
36327. Imperfect specimen, showing some of the spines ; Orkney. 
Purchased, 1862. 
39190-91. Two very indistinctly preserved specimens; Skaill, 
Orkney. Bowerbank Coll, 
41843-44. Two similar fossils ; Orkney. Purchased , 1869. 
P. 1357-9. Seven specimens, very imperfect; Belyacreugh and 
Bamna Gio, Orkney. Egerton Coll. 
P. 3261. Trunk with caudal extremity; Belyacreugh. 
Enniskillen Coll. 
Diplacanthus longispinus, Agassiz. 
[Plate III. fig. 1.] 
1841. “ Ichthyolite,” H. Miller, Old Red Sandstone, pi. viii. fig. 1. 
1844. Diplacanthus longispinus , L. Agassiz, Poiss. Foss. V. G. R. pp. 
34, 42, pi. xiii. fig. 5, pi. xiv. figs. 8, 9. 
1848. Diplacanthus perarmatus, F. M'Coy, Ann. Mag. Nat. Hist. [21 
vol. ii. p. 301. [Woodwardian Museum, Cambridge.] 
1855. Diplacanthus perarmatus , F. M‘Coy, Brit. Palaeoz. Foss, p 585 
pi. iin. fig. 3. 
1888. Rhadinacanthus longispinus , R. H. Traquair, Geol. Mag. [3] 
vol. v. p. 512. M ,/. 
Type. Nearly complete fish : Fom^ Museum/^'^ A/ ^^‘ 
A large species, attaining a maximum length of about 0*22. 
Body robust, but elongated, the greatest depth being contained 
about four and a half times in the total length. Fin-spines much 
elongated, with at least one longitudinal sulcus parallel to the ante¬ 
rior margin. Pectoral fin-spines about one third larger than the 
pelvic pair, and the median pectorals relatively small, well separated 
from the ordinary pectorals; pelvic fins situated much nearer to the 
anal than to the pectorals. Dorsal fin-spines very large and elon¬ 
gated, the first smaller than the second, placed slightly behind the 
pectoral arch; second dorsal opposed to the anal and much larger 
than the latter. Scales marked with prominent radiating furrows 
and ridges. 
This species is regarded as the type of a distinct genus, Rhadina¬ 
canthus , by Traquair, on the assumption that median pectoral spines 
are absent. A specimen recorded below (No. P. 4041), however, 
proves that the spines in question occur in their usual place; and 
