344 THE OSTRACODERMS AND THE MARINE ARACHNIDS. 



structure of the shell of these animals, and concluded that they were not crusta- 

 ceans, he entirely ignored the existence of the eye tubercles, although their pres- 

 ence afforded very weighty evidence against his conclusion. 



Huxley (1858, page 277) in reply to Agassiz, who had remarked on the 

 singular resemblance between the shell of C. lloydii and that of crustaceans, and 

 to Roemer's and Kunth's opinion that Pteraspis was a crustacean, seems to have 

 closed the discussion for the time with his oft-quoted statement that ''No one can, 

 I think, hesitate in placing Pteraspis among fishes. So far from its structure 

 having 'no parallel among fishes,' it has absolutely no parallel in any other divi- 

 sion of the animal kingdom. I have never seen any molluscan or crustacean 

 structure with which it could be for a moment confounded." 



Roemer accepts these statements apparently because they came from Huxley, 

 although he does not make an unconditional surrender of his opinion, for he says 

 "Allerdings manche Analogic der aiisseren Form mit Crustacean-Formen dar 

 bieten wurde." 



In 1864, Lankester divided the pteraspidag into the three genera, Pteraspis, 

 Cyathaspis and Scaphaspis. But in 1872, Kunth described a shield of Cyathaspis, 

 below which he found one belonging to Lankester's genus Scaphaspis, and he 

 rightly concluded that the two shields belonged to the same animal. He main- 

 tained that the lower shield bore the same relation to the upper one that the tail 

 plate of a rolled up trilobite does to its head shield, and that between the two were 

 a number of pieces comparable with the segmental trunk plates of a trilobite. 

 Other plates were present which Kunth regarded as locomotor organs, or foot- 

 jaws. From the above facts Kunth concluded that these remains were not those 

 of a fish, but of an arthropod. In referring to Huxley's statement that there is no 

 molluscan or crustacean structure with which such remains could be for a moment 

 confounded, and to Kner's belief that Scaphaspis was the shell of Sepia officinalis, 

 Kunth adds "so schienen mir diese Ansichten in verein mit unserem vorliegenden 

 Stiicks mir zu beweisen dass wir es mit einer Crustacean Abtheilung von ganz 

 eigenthiimlicher Schalstructur zu thun haben. Denn jedenfalls giebt es weder 

 einen Fisch noch eine Sepien Schulpe, die eine ahnliche Structur wie die Schilder 

 zeigte; wohl aber ist die Organization des ganzen Stiickes beweisend fur Crus- 

 taceen Character" (page 6). 



Both Schmidt (1873, page 330) and von Alth (page 47) agree with Kunth 

 that Scaphaspis is the ventral shield of Pteraspis, but they deny that any of the 

 remains described as Pteraspis, Cyathaspis or Scaphaspis are crustaceans, 

 although no valid reasons are given for doing so. 



Lankester (1868, page 26) admitted the presence in Cyathaspis of tubercles 

 corresponding with similar tubercles in Pteraspis, which are "produced by the 

 supposed orbits;" but how a vertebrate eye, or an "orbit," could be preserved as 

 a beautifully rounded protuberance when all the other soft parts are completely 

 destroyed, is not discussed. 



Lankester attached much importance to the presence of scales on the anterior 



