No. 444.] PTEHASPIDAZ AND CEPHALA SP/DAS, 



specialized appendages like those of Pterichthys, with their 

 necessarily complex arrangement of muscles and nerves, then 

 the elaborate discussions over the origin of the paired append- 

 ages of higher vertebrates would seem to be a waste of time. 

 But some such explanation as that offered by Dean is forced on 

 those who regard these animals as true fishes by the difficulty, 

 from their point of view, in explaining the presence of so many 

 different kinds of appendages in a vertebrate head, for it is 

 generally assumed that the appendages of Pterichthys are not 

 homologous with those of Cephalaspis, and that neither one nor 

 the other are homologous with true pectoral fins. 1 



The Fringing Processes. — Lankester showed long ago, in his 

 reconstruction of Cephalaspis, a fringe of peculiar plates along 

 the ventral margins of the trunk, which, although they produced 

 a most unusual appearance, have not attracted the attention 

 they deserve. Whatever their significance may be, there is 

 apparently nothing known in true fishes that is exactly compar- 

 able with them. 



In one specimen belonging to the Powrie collection in the 

 Edinburgh Museum (No. 163) the body was badly crushed, 

 throwing the plates t<> one side where they la\ flatwise and well 

 separated. On examination with a lens, some of the plates 

 appeared to consist of at least two joints, possibly three, the 

 distal one being the smallest. The surfaces of the plates were 

 covered with coarse spines. The details of this specimen were 

 not brought out by the photographs with sufficient clearness to 

 allow them to be reproduced. 



In the beautiful Ledbury specimens of Cephalaspis mierchisoni, 

 described by Woodward, the fringes are clearly seen in various 

 positions, either from the sides or from below (PI. I, Figs. 1 and 

 5.) In most cases they form a series of regularly overlapping, 

 oblong plates, apparently in their normal position on the ventral 

 margin of the trunk. Each plate appears to be three lobed, the 

 segmentation being indicated by the gently rounded outline of 

 each joint, as well as by the transverse lines that separate one 



