THE DEVONIAN ROCKS OF CANADA. 105 
the labial appendages indicated by dotted lines on Agassiz’s ideal restoration of the genus 
Pterichthys, on Plate VI. Fig. 1, of the Atlas to the “ Monographie des Poissons du Vieux 
Grès Rouge.” This explanation of these appearances, however, seems to be no longer 
tenable, and it is, perhaps, more likely that these supposed labial appendages are merely 
worn and badly preserved casts of the lateral terminal plates. On each side of the orbital 
opening, also, in two or three similar casts of the same species, there isa slightly prominent 
but flattened conical elevation or protuberance, which diverges obliquely forward and 
outward. These, the writer was at one time disposed to consider, might represent a pair 
of dermal processes on the outside of the cranial shield, but a more attentive study has led 
to the conclusion that they are merely depressions of corresponding shape on the interior 
of the test, which leave little or no traces on its exterior. 
No vestiges of the tail or of any of the fins, other than the two pectoral spines, have 
yet been detected, and no traces of any true bony jaw have yet been recognized. Professor 
E. D. Cope, who has examined numerous specimens of this species, distinctly states that 
it has no lower jaw, and the writer is of the same opinion. 
An average and apparently adult example is of the following dimensions: length 
of the united cranial and dorsal shields along the median line, about six inches; 
maximum breadth of the same, three inches and three quarters; length of pectoral spines, 
not quite five inches. A detached pectoral spine, however, has been collected, which 
is six inches and three-quarters long, and more or less isolated plates show that the 
species may have occasionally attained to slightly larger size than that indicated by this 
pectoral. 
A single mould or impression of the ventral surface of a specimen of this species, 
with one of the pectoral spines in place, was discovered by Mr. R. W. Ells (of the Geo- 
logical Survey of Canada) in the summer of 1879. The much better specimens upon which 
the description in the “ American Journal of Science and Arts,” was based, were collected 
by Messrs. Ells and T. C. Weston, inthe months of June and July of the following year. 
Since then, including fragments, which are very instructive, between two and three 
hundred examples of the same species were collected by Mr. A. H. Foord, which, with 
those already in the Survey collection, have formed the material from which the present 
description was made. 
To quote the words of Prof. Owen :—‘“ The fossil remains of the singular fishes of the 
extinct order Placoganoidei were first discovered about 1813, in formations of the ‘ old red’ 
or Devonian age in Russia, and are preserved in museums at St. Petersburg and Dorpat. 
The relations of these specimens to the class of fishes was first announced by Professor 
Asmuss,” in 1840, “and, shortly after, the generic names As/erolepis and Bothriolepis were 
invented by Professor Eichwald to express certain modifications of the external surface of 
portions of the ganoid plates, subsequently recognized as constituting the buckler of the 
fore-part of these extinct fishes. In September, 1840, Hugh Miller submitted to the Geo- 
logical section of the British Association at Glasgow the first discovered specimens which 
afforded a recognizable idea of the form of one of these ‘old red’ fishes, and for this form 
Professor Agassiz assigned the generic name Plerichthys (pteron, a wing, ichthus, a fish). 
Although, therefore, the term Asferolepis had been attached to a fragment of the cuirass of 
this fish a few months previously, yet, as no recognizable generic characters were associated 
with such name, and as Asferolepis has been applied also to other genera—e. g., Homostius 
Sec. IV., 1886. 14. 
