No. 444.] P TERA SPIDsE AND CEP HA LAS PI DjE. 



835 



ml organism. The scales are fish-like. I know no Arthropod, 

 nor any other organism except a fish which possesses any struc- 

 ture even remotely representing them." "The shields of the 

 Chitonidae and Cerripedae are the only animal structures, except 

 the scales of a ganoid fish (with which they agree exactly) which 

 they could even vaguely suggest.*' " The form of this shield, 

 and its details as to apertures, processes, etc., agrees with the 

 view that it belongs to a fish most fully. It has not the 

 remotest suggestion of Crustacean affinities about it." 



After commenting on the fact that the fossil in question was 

 marked with long parallel striae, and that the middle layer con- 

 tained the polygonal cavities he adds ('64, p. 195), " This 

 structure, which has no parallel among fishes, or, indeed, any 

 group of the animal kingdom, leaves no possibility of a doubt 

 that the specimen is a fragment of Pteraspis." .... Lankester 

 further maintains ('68, p. 4) that by the discovery of these scales 

 "the piscine nature of these fossils was definitely set at rest." 



These positive statements are somewhat contradictory and 

 would now be hardly warranted by the facts of the case. The 

 crustacean character of the shields has been repeatedly com- 

 mented on by competent observers. In his own monograph 

 (p. 61) he has described a fragment, possibly connected with 

 Cephalaspis which he names Kallostrakon podura (Tolypelepis ?) 

 « on account of the resemblance to the well-known microscopic 

 markings of the scales of the insect Podura." 



It is not true that there are no arthropods with structures 

 even remotely resembling these scales, because in Pterygotus the 

 entire body is covered with an ornamentation which bears an 

 astonishing resemblance to fish scales, so much so as to deceive 

 such a keen observer of fishes as Louis Agassiz. Moreover in 

 manv trilobites and in the Ceratiocarina, Clarke, the surface 



of the shell is ornamented with ridges 

 those of Pteraspis in external appcaran. 



these statements 

 sn acquainted with 



agreed that it i 

 its microscopic 



