468 Notices of Memoirs — Dr. R. E. Traquair's Address. 



Here we have a creature whose general form reminds us strongly 

 of Thelodus, but whose close affinity to Cephalaspis is absolutely 

 plain, were it only on account of the indications of orbits on the top 

 of the head. 



The expanded anterior part which here represents the head-shield 

 of Cephalaspts shows not the slightest trace of cornua, but forms 

 posteriorly a gently rounded lobe on each side, clearly suggesting 

 that the cornual flaps of Cephalaspis are homologous with and 

 derivable from the lateral expanses in the CoelolepidEe. This cephalic 

 covering is composed of numerous small polygonal plates like those 

 of which the head-shield in Cephalaspis no doubt originally con- 

 sisted, and the minute tubercles which cover their outer surfaces 

 also suggest that the superficial layer was formed by the fusion 

 of Coelolepid scales. The body is covered with rhombic scales, 

 sculptured externally with tubercles and wavy transverse ridges, 

 and arranged in lines having the same general direction as the scutes 

 of Cephalaspis, from which we may infer that the latter originated 

 from the fusion of scales of similar form. The fins are as in 

 Cephalaspis, there being one small dorsal situated far back, and 

 a heterocercal caudal, which is triangular in shape, and not deeply 

 cleft into upper and lower lobes as in the Ccelolepidse. Finally, the 

 scales, on microscopic examination, show well-developed bone lacunee 

 in their internal structure. 



That Ateleaspis belongs to the Osteostraci there is thus not the 

 smallest doubt, but its general resemblance to the Ccelolepidae in its 

 contour anteriorly led me to regard it as an annectent form, and 

 consequently to believe that there is after all a genuine genetic con- 

 nection between the Heterostraci and the Osteostraci. And I have 

 not seen reason to depart from that opinion even though Ateleaspis 

 turns out to be still closer to Cephalaspis than was apparent in the 

 original specimens. 



If this be so, then Cephalaspis, as well as Pteraspis and its allies, 

 is traceable to the CoelolepidEe, shark-like creatures in which, as we 

 have already seen, the dermal covering consists of small shagreen- 

 like scales, or of minute hollow spines, and consequently all theories 

 as to the arthropod origin of the Ostracodermi, so far as they are 

 founded on the external configuration of the carapace in the more 

 specialized forms, must fall to the ground. And from the close 

 resemblance of these scales of Thelodus to Elasmobranch shagreen 

 bodies — for forty-five years they had been, by most authors, actually 

 referred to the Selachii — I concluded that the Coelolepidfe owed their 

 origin to some form of primitive Elasmobranchs, That is, however, 

 not in accordance with the view of the late Professor Cope, that the 

 Ostracodermi are more related to the Marsipobranchii, and that, from 

 the apparent absence of lower jaw, they should be placed along with 

 the last-named group in a class of Agnatha, altogether apart from 

 the fishes proper. And Dr. Smith Woodward, who is inclined to 

 favour Cope's theory, has expressed his view that the similarity of 

 the Coelolepid scales to Elasmobranch shagreen is no proof of an 

 Elasmobranch derivation, but that such structures, representing the 



