Dr. Rk. H. Traquair—Old Red Sandstone Fishes. 509 
together an instructive series of its remains, from which it appears 
that the head and arms closely resembled those of <Asterolepis and 
Pterichthys, the limbs being very short, and scarcely reaching beyond 
the lozenge-shaped median plate of the ventral surface. As a species 
it is distinguished by the excessive narrowness of the anterior 
margin of the anterior median dorsal plate, which consequently 
assumes an almost pointed lanceolate contour. 
Species of Pterichthys.—I would arrange the British species of 
Pterichthys as follows : 
A. Terminal division of arm slender, tapering. 
1. Pterichthys Milleri, Ag. (including P. latus, Ag.). Inferior surface of 
carapace broadly ovate. 
2. P. quadratus, Eger. Inferior surface of carapace peculiarly short in 
proportion to its breadth. 
3. P. cornutus, Ag. (including P, testudinarius, Ag.). Inferior surface of 
carapace narrowly ovate. 
B. Terminal division of arm expanded, abruptly pointed. 
4. Pterichthys productus, Ag. (including P. cancriformis, Ag.). Inferior 
surface of carapace narrowly ovate. 
5. P. oblongus, Ag. Inferior surface of carapace long and narrow, sides 
nearly straight. 
As the distinctions of form indicated above are actual, and not 
the result of mere distortion by crushing, I have thought it desirable 
to retain the groups represented by them as distinct species. Yet 
so closely do they represent each other in other respects, that very 
possibly they may only be entitled to rank as varieties. Before 
coming to these conclusions, I have examined a very large number 
of specimens in various museums, including all the types save that 
of Pterichthys quadratus, Egert. 
Before leaving the subject of Pterichthys I may state that I have 
examined the specimen in the Egerton Collection, British Museum, 
on which Sir P. Egerton founded his opinion that a pair of ventral 
fins were present in this genus, and find that the two supposed 
ventrals are only two portions of the dorsal separated by a little 
dislocation or fault, a phenomenon of by no means uncommon occur- 
rence in nodules. 
Bothriolepis, Hichwald.—When Pander wrote his well-known 
“ Placodermen,” he was unacquainted with the structure of Bothrio- 
lepis, else he would not have included it with Pterichthys as one of 
the synonyms of Asterolepis. The dorsal plate figured by Hichwald 
as belonging to Bothriolepis ornatus' marks it as one of a group of 
species, which we now know from Russia, from Great Britain, and 
from Canada, and whose generic distinctions both from Asterolepis and 
Pterichthys are of the most salient kind. Most of these distinctions 
were pointed out by Lahusen and by Trautschold,? but our know- 
ledge of the genus has also been largely increased by the discovery 
of numerous well-preserved individuals of a Canadian species, which 
has been figured and described by Whiteaves under the name of 
Pterichthys (Bothriolepis) Canadensis.* 
1 Lethzea Rossica, tab. 56, fig. 3. 
* Ueber Bothriolepis Panderi, Lahusen, Bull. Imp. Mose. vol. 55, pt. 2 (1880), 
pp. 169-179. 3 Trans. Roy. Soc. Canada, pp. 101-107. 
