256 Br. JR. H. Tmquair — On Diplacanthus, sp. nov. 



thidse two dorsal fins and clavicles present. Of course in the 

 Acantbodidse and Ischnacanthidss the ossicle supporting the pectoral 

 spine is interpreted as a basal piece. 



Against this view of Mr. Smith Woodward I protested in a 

 review of his work which appeared in this Magazine for March 

 1891, and I am still as strongly as ever of opinion that the element 

 which Mr. Woodward calls "clavicle" in Diplacanthus is identical 

 with that which he considers as " basal cartilage " in Acanthodes 

 and Ischnacanthus. And I base this opinion upon the fact that the 

 relation of the supposed basal bone, in the one case, to the pectoral 

 spine, is identical with that of the supposed clavicle in the other ; 

 while we may also, in the series of Acanthodian genera, trace every 

 gradation from the most to the least claviculoid shape of the bone. 



No one can doubt that the Diplacanthidee show a more archaic 

 type of configuration than the Acanthodidse, and among the former 

 the most archaic form is Climatius. Here the ossicle in question 

 greatly resembles the vertical limb or upper part of a palgeoniscid 

 clavicle, being both thin and flattened, and I have not been able to 

 discover in the specimens before me any trace of the internal tubular 

 hollow seen in Acanthodes} In front of the lower end there is au 

 infra-clavicular element. 



So there is also in Parexus, but in this genus the internal hollow 

 has appeared in the supporting ossicle of the spine, which, though 

 still expanded and flattened below, has become straighter and moi"e 

 cylindrical above, thus showing a decided step towards the " basal " 

 bone of Acanthodes. And, indeed, as " basal cartilage " this very 

 element is designated in Mr. Woodward's diagram of the shoulder of 

 Parexus (op. cit, p. 35), while the piece on the same figure which 

 he designates " clavicle " seems to me, from its position with 

 respect to the anterior extremity of the spine, and also the other 

 element just referred to, infra-clavicular in its nature. This view 

 receives further confirmation from the fact mentioned by Mr. 

 Woodward that these supposed clavicles meet in the middle line. 

 In Diplacanthus the supporting bone of the great pectoral spine 

 becomes again very claviculoid in shape, but the internal tubular 

 hollow is there all the same, a fact noticed by Mr. Woodward himself 

 (op. cit. p. 23). A pair of infra-clavicular elements is also seen, as 

 already noticed, and these help to support the lesser pectoral spines. 



Concerning the relations of the two pectoral spines of this genus, 

 outer and inner, Mr. Woodward says that their axes " are inclined 

 towards one another, and at their proximal extremity they are firmly 

 united by a mass of hard tissue, which is probably to be regarded as 

 the basipterygium or basal cartilage." This is a view with which 

 I cannot agree. In the first place, even if the tissue in question 

 were cartilage, I do not see any resemblance between it and the 

 ossicle, which the author interprets as " basal " cartilage, in Acan- 

 thodes. But the appearance is, to my eye, solely due to an expansion 



^ Since the above has been in type, I have seen in specimens of Climatius, preserved 

 in the British Museum, clear evidence that in this genus the bone in question is 

 furnished with an internal tubular hollow, as in other Acanthodei. 



