•_>1 |. Frederick Chapman: 



Structure and Condition of the Rock in which Phlycfaenaspis 



australis was embedded '. 



The holotype described by McCoy, and the accompanying speci- 

 men, was found in a pale chocolate-coloured, fine-grained mud- 

 stone. The onlv other organic remains to be seen in these hand 

 specimens are fragments and impressions of the common Middle 

 Devonian Spirifer, S. yassensis ( = S. laevicostata , McCoy, non 

 Valenciennes). 



The variety, confertituberculata, occurs on a weathered surface 

 of hard, nearly black bituminous limestone full of the remains of 

 Spirifer yassensis; a low power shows the matrix to contain numbers 

 of small ostracoda, probably belonging to the genus Primitia. 



Ostracoda seem to have formed part of the food supply of these- 

 early palaeozoic fishes, and it is interesting to notice in this respect 

 that the rock in which the National Museum specimens of Phlyc- 

 taenaspis acadica are found, literally swarms with several genera 

 of ostracoda. including IKloedenella and ILeperditia. 



Phlyctaenaspis was evidently more at home in the muddy Devonian 

 sea with its accompanying crustacean and brachiopod life than in 

 the clearer waters where the coral fauna existed. 



EXPLANATION OF PLATES. 

 Plate XX. 



Pig. 1. — Phlyctaenaspis australis, McCoy sp. Holotype of "Aster- 

 olepis ornata, var. australis," McCoy. Middle Devo- 

 nian. Buchan, Cippsland, Victoria. Cir. nat. size. 



Fig- 2. — Phlyctaenaspis australis, McCoy sp. Specimen showing a 

 natural impression of the tuberculated plates of the 

 cranial shield. Middle Devonian. Buchan. Cippsland. 

 Cir. nat. size. 



Fig. 3.- Diagram of plates of cranial shield of Phlyctaenaspis- 

 anglica, Traquair; with outline of holotype of P. 

 australis (shaded) to show relative area. 



Fig I Phlyctaenaspis australis, McCoy, var. confertituberculata, 

 var. iiov. An almost complete cranial shield. Middle 

 Devonian. Buchan, Gippsland. Cir. nat. size. 



