I. Introduction. 
Of all the families usually included in the problematical and heterogeneous group of 
animais called the Ostracoderms, noue is more interesting to the morphologists tlian the 
Tremataspidae, as what little we know about tliem shows they possessed a most extraordinary 
structure, unlike in many respects that of any other group of animais. 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 hâve long been a source of perplexity to the paleontologist, clearly point to 
tlieir affinity with Arthropods like Famulus, Apus, and the Trilobites. 1 ) 
The importance of the Tremataspidae to the morphologist 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 
ail tlieir hard parts. This knowledge will certainly throw much light on the morphology of 
the whole group of Ostracoderms and may afford décisive evidence of the genetic relation- 
ship between the Yertebrates and Invertebrates. 
Rohon lias entertained a similar view of the importance of Tremataspis, for lie says, 
92, p.37, «Es ist meine volle Ueberzeugung, dass diese Gattung berufen sei, bei 
den künftighin mit Hilfe eines zahlreicheren Materials zu unternehmenden 
stammesgeschichtlichen Studien über niedere Fische eine sehr bedeutende 
Rolle zu spielen.» 
1) Ünfortunately, the animal morphologists, or the 
embryologists dealing with broad phylogenetic problème 
have not as a rule allowed a considération of this remark- 
able group of animais to alter the form of crystallization 
into which their views on the relation of Vertebrates to 
Invertebrates have fallen. When I have been privilcged 
3au. Фпз.-Мат. Отд. 
to discuss this subject with morphologists having decided 
opinions on the origin of Yertebrates, 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! 
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