I. Introduction. 



Of all the families usually included in the problematical and heterogeneous group of 

 animals called the Ostracoderms, none is more interesting to the raorphologists than the 

 Tremataspidae, as what little we know about them shows they possessed a most extraordinary 

 structure, unlike in many respects that of any other group of animals. While the character 

 of the trunk scales, of the orbits and other sensory openings, the minute structure of the 

 shell, and the presence of the lateral line system, — clearly indicate the affinity of Trema- 

 taspis with Pteraspis, Gephalaspis and Pterichthys, and through them with the true Ver- 

 tebrates; other features, such as the general shape of the shield and its more superficial 

 texture, which have long been a source of perplexity to the paleontologist, clearly point to 

 their affinity with Arthropods like Limulus, Apus, and the Trilobites. ^) 



The importance of the Tremataspidae to the raorphologist also lies in the fact that 

 while the specimens are rare and more or less fragmentary, they are usually well preserved 

 and give fair promise that ultimately we shall be able to decipher in detail the structure of 

 all their hard parts. This knowledge will certainly throw much light on the morphology of 

 the whole group of Ostracoderms and may afford decisive evidence of the genetic relation- 

 ship between the Vertebrates and Invertebrates. 



Rohon has entertained a similar view of the importance of Tremataspis, for he says, 

 92, p. 37, «Es ist meine voile Ueberzeugung, dass diese Gattung berufen sei, bei 

 den kiinftighin mit Hilfe eines zahlreicheren Materials zu unternehmcnden 

 stammesgeschichtlichen Studien tiber niedere Fische eine sehr bedeutende 

 Rolle zu spielen.)) 



1) Unfortunately, the animal niorphologists, or the 

 embryologista dealing with broad phylogenetic problems 

 have not as a rule allowed a consideration of this remark- 

 able group of animals to alter the form of crystallization 

 into which their views on the relation of Vertebrates to 

 Invertebrates have fallen. When I have been privileged 



to discuss this subject with morphologists' having decided 

 opinions on the origin of Vertebrates, the discussion has 

 often ended with a request for information as to what the 

 Ostracoderms looked like, for they were not quite sure 

 whether they belonged to the Arthropods, or the true 

 Vertebrates! 



3au. 4iia.-MaT. Ota. ^ 



