6 Dr. H. Woodward — Note on an Ichthyodorulite. 



Amongst recent plagiostomous fishes I do not find any one species 

 with spines at all comparable in the least degree with the type of 

 Edestus. If it be permissible to interpret the Australian fossil to be 

 the impression of the spine of the pectoral fin of an Edestus-Yike 

 fish, there are numerous examples of living Siluroid fishes with 

 powerful pectoral fin-spines, some of which at least have denticles 

 upon the outer as well as the inner edge of the spine, although none 

 are so highly curved as the Gascoyne fossil. Arius rita, of the river 

 Ganges, has denticles on both edges of its pectoral spines ; so also 

 has Aspredo Icems (Woodcut, p. 5, Fig. 2), from Surinam ; Synodontis 

 omias, and Auchenaspis falcarius, from West Africa ; Arius falcarius, 

 Formosa ; and Silurus giants, from Lake Derkos ; Doras, sp., from 

 South America (Woodcut, p. 5. Fig. 3), and many others. 



It is difficult to imagine any fish with a pectoral spine curved to 

 so great a degree as is this Australian ichthyodorulite, but on the 

 other hand it seems improbable that it was a median dorsal defence. 



To quote again from Prof. Newberry : — "The segmented structure 

 of the fossil is its most marked and anomalous feature, but one 

 equally so, whether it be considered spine or jaw, and for which no 

 parallel suggests itself. It is undoubtedly to this structure that we 

 must ascribe the absence of a large medullary cavity, as each 

 segment seems to have been nourished somewhat independently of 

 its fellows. 



" It is also evident that this spine was implanted in the integu- 

 ment at a low angle, and that an investing skin or other nutrient 

 tissue covered fully half its surface, on the lower portion reaching 

 up to the enamelled bases of the denticles. This is the relative 

 position of the defensive spines of Kays, to which an analogy is 

 suggested by this character. 



" In some plagiostomous fishes, a bone is found quite buried in the 

 integuments of the back, and which is a rudimentary representative 

 of a posterior dorsal fin ; it is, therefore, not impossible that we 

 have in the fossil before us, a higher development and special 

 modification of that organ." (Newberry and Worthen, op. cit. p. 352.) 



Keferring again to the valuable and suggestive memoir by Prof. 

 E. D. Cope on Pelecopterus quoted above (p. 4), I cannot but think 

 that it affords the most probable explanation of the anomalous 

 structure in Edestus. 



" The entire pectoral fin," says Cope, " so far as it is known, is 

 devoted to the construction of a powerful spine." " The spine is 

 composed of parallel rods in close apposition. The anterior edge, 

 being oblique, the exti'emities of the rods terminate successively at 

 the border, which is trenchant, constituting the offensive part of 

 the spine." 



It appears to me to be only necessary that the ' parallel rods ' 

 composing the spine of Pelecopterus should be bent into curves, 

 corresponding to the segmentation seen in Edestus, and we at once 

 have a solution of the peculiar structure in the latter. 



If this interpretation be accepted, then Edestus must be deemed to 

 be, like Pelecopterus, a modified pectoral fin-spine, composed of a 



