RELATIONSHIP OF AMMOCGTES TO OSTRACODERMS 351 
appendages. At present we have not sufficient evidence to decide 
this question. 
That the animal crawled about in the mud by means of free 
appendages is by no means an impossible view, seeing how difficult 
it is to find the remains of appendages in the fossils of this far-back 
time, even when we are sure that they existed. Thus, for many 
generations, the appendages of trilobites, which occur in such count- 
less numbers, and in such great variety of form, were absolutely 
unknown, until at last, in consequence of a fortunate infiltration 
by pyrites, they were found by Beecher preserved down to the 
minutest detail. Even to this day no trace of appendages has been 
found in such forms as Hemiaspis, Bunodes, Belinurus, Prestwichia. 
The whole question of the evidence of any prosomatic appendages 
in these ancient fishes is one of very great interest, and of late years 
has been investigated by Patten. It has long been known that 
forms such as Pterichthys and Bothriolepis possessed two large, jointed 
locomotor appendages, and Patten has lately obtained better speci- 
mens of Bothriolepis than have ever been found before, which show 
not only the general configuration of the fish, but also the presence 
of mandibles or gnathites in the mouth-region resembling those of 
an arthropod. These mandibles had been seen before (Smith Wood- 
ward), but Patten’s specimens are more perfect than any previously 
described, and cause him to conclude that these ancient fish were 
of the nature of arthropods rather than of vertebrates. 
Patten has also been able to obtain some excellent specimens of 
the under surface of the head of Tremataspis, which, as evident in 
Fig. 148, show the presence of a series of holes, ranging on each side 
from the mouth-opening, in a semicircular fashion towards the middle 
line. He considers that these openings indicate the attachments of 
appendages, in opposition to other observers, such as Jaekel, who look 
upon them as gill-slits. To my mind, they are not in the right 
position for gill-slits; they are certainly in a prosomatic rather than 
in a mesosomatic position, and I should not be at all surprised if 
further research justified Patten’s position. So convinced is he of 
the presence of appendages in all these old forms, that he considers 
them to be arthropods rather than vertebrates, although, at the same 
time, he looks upon them as indicating the origin of vertebrates from 
arthropods. Here, perhaps, it is advisable to say a- few words on 
Patten’s attitude towards this question. 
