| Fig. 14.—Dorsal Head-shield of Thyestes (Auchenaspis) verrucosus. (From Rohon.) Fro., narial opening; l.e., lateral eyes; gl., glabellum or plate over brain; Occ., occipital region. | Fig. 15.—Pterichthys. |
In a later chapter I propose to discuss the peculiarities and the nature of the head-shields of these earliest fishes, in connection with the question of the affinities of the animals which bore them. At this point of my argument I want simply to draw attention to the undoubted fact of the striking similarity in appearance between the earliest fishes and members of the Palæostraca, the dominant race of arthropods which swarmed in the sea at the time: a similarity which could never have been suspected by any amount of investigation among living forms, but is immediately revealed when the ages themselves are questioned.
Fig. 16.—Bothriolepis. (After Patten.)
An., position of anus.
I have not reproduced any of the attempted restorations of these old forms, as usually given in the text-books, because all such restorations possess a large element of fancy, due to the personal bias of the observer. I have put in Rohon's idea of the general shape of Tremataspis (Fig. [17]) in order to draw attention to the lamprey-like appearance of the fish according to his researches (cf. Fig. [18]).
Fig. 17.—Restoration of Tremataspis. (After Rohon, slightly modified.)
Fig. 18.—Ammocœtes.