﻿26 ACANTHODII. 



43018. Specimen assigned to D. crassispinus by Agassiz, op. tit. 

 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. BowerbanJc Coll, 



41843-44. Two similar fossils : Orkney. Purchased, 1869. 



P. 1357-9. Seven specimens, very imperfect ; Belyacreugh and 

 Ramna Gio, Orkney. Egerton Coll. 



P. 3261. Trunk with caudal extremity; Eelyacreugh. 



Ennishillen 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. [2] 



vol. ii. p. 301. [Woodwardian Museum, Cambridge.] 

 1855. Diplacanthus perarmatus, F. M'Coy, Brit. Palaeoz. Foss. p. 585, 



pi. iiB. fig. 3. 

 1888. Rhadinacanthus longispinus, R. H. Traquair, Geol. Mag. [3] 



vol. y. p. 512. 



Type. Nearly complete fish ; Forres Museum. 



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 



