6o2 • NATURAL SCIENCE. o^- 



already treated. They are commonly regarded as homologous with 

 the paired pectoral fins of fishes, and certainly in their mode of 

 fixation to the trunk there is much to favour that supposition ; but 

 the recent discovery (13) of an allied organism, Acanthaspis, in the 

 Lower Devonian of Spitzbergen, suggests the wisdom of suspending" 

 judgment. The dorsal body-shield of Acanthaspis is simpler than 

 that of Pterichthys ; but the arrangement of the plates on the ventral 

 aspect (Fig. 8) is identical, and there are also hollow pectoral 

 appendages. These appendages, however, are merely simple 

 triangular spines {(ip.) firmly fixed by suture to processes of the 

 body-armour {pr.) ; and if they are an inferior or special condition 

 of the ordinarily moveable arms, it seems not unlikely that those 

 arms will prove to be different in origin from the paired limbs of 

 fishes. 



In conclusion, it may be said that recent researches tend towards 

 demonstrating the antiquity of the race of lampreys and hag-fishes ; 

 and evidence is accumulating to show that a great group of limbless,, 

 armoured Chordata formed a conspicuous feature in early Palaeozoic 

 life. Beyond this statement, however, we cannot yet advance, and 

 much has still to be learned even concerning those few organisms 

 whose main features have already been elucidated. 



REFERENCES. 



1. Alth, A. von. — Ueber die palaozoischen Gebilde Podoliens und deren 



Versteinerungen. Abh. k.k. geol. Reichsanst. Wien., vol. vii., no. i (1874). 



2. Ueber die Zusammengehorigkeit der den Fischgattungen Pteraspis, 



Cyathaspis, und Scaphaspis zugeschriebenen Schilder. Beitr. Paldont. Oestr.- 

 Ungarns, vol. ii. (18S6). . 



3. Lankester, B. Ray. — The Cephalaspidae. Monogr. Palaont. Soc. {iS6S~yo). 



4. Pander, C. H. — Die Placodermen des devonischen Systems (1857). 



5. Rohon, J. V. — Ueber untersilurischeFische. Bull. Acad. Imp. Set. St. Pitersbourg,. 



vol. xxxiii., p. 269 (1889). 



6. Die obersilurischen Fishe von Oesel. Mini. Acad. Imp. Set. St, 



Petersbourg, ser. 7, vol. xxxviii., no 13 (1892). 



7. Selenka, E. — Das Stirnorgan der Wirbeltiere. Biol. Centralbl., vol. x., p. 324 



(1891). 



8. Traquair, R. H. — On the Structure and Classification of the Asterolepidas, 



Anil. Mag. Nat. Hist., ser. 6, vol. ii., p. 485 (1888). 



9. On the Fossil Fishes found at Achanarras Quarry, Caithness. Ibid.,. 



vol. vi., p. 485 (1890). 



10. 'Walcott, C. D. — Note in Amer. Jovrn. Sei., ser. 3, vol. xli., p. 245 (1891). 



11. Preliminary Notes on the Discovery of a Vertebrate Fauna in Silurian 



(Ordovician) Strata. Bull. Geol. Soc. Ameriea, vol. iii., p. 153 (1892). 



12. Woodward, A. S. — Catalogue of Fossil Fishes in the British Museum,. 



Part II. (1891). 

 13. On the Devonian Fish-fauna of Spitzbergen. Ann. Mag. Nat. Hist., ser. 



G, vol. viii., p. I (1891). 

 14. On the Lower Devonian Fish-fauna of Campbellton, New Brunswick. 



Geol. Mag., dec. 3, vol. ix., p. i (1S92). 



A. Smith Woodward. 



