FISHES OF THE DEVONIAN AGE. 53 
only many new things, but what will perhaps be more instructive, the 
missing parts of organisms but imperfectly represented in the collections 
hitherto made. Among these, portions of the structure of Acanthaspis, Acan- 
tholepis, and Coccosteus may be mentioned as special desiderata. 
Order CROSSOPTERYGID&. 
Genus ONYCHODUS, Newb. 
Ganoid fishes of large size; cranium composed of a large number of 
bony plates covered with enamel and tuberculated; tuberculation relatively 
fine, and formed by what may be compared to small grooved cones, pressed 
down and adherent; jaws set with numerous conical, acute, more or less 
recurved teeth of nearly uniform size; maxillary forming a low triangle, 
with much produced acute lateral angles; dentary bones posteriorly acute, 
where they are overlapped by the articular portions of the mandibles, long 
and narrow, curving upward to the symphysis, where they support an 
intermandibular arch of bone, to which was attached a single series of 
large, curved, conical teeth; teeth all smooth, covered with enamel, without 
basal plications; those of the maxillaries and mandibles implanted in sockets 
or anchylosed. The teeth of the median crest are seven or eight in number, 
attached (by ligaments?) to an arched base, from which they radiate. 
They are much curved, often sigmoidally, have a circular section near the 
summit, are somewhat compressed below, and expand at base into several 
prominent roots or tuberosities. They have a central cavity extending 
nearly to the point, surrounded by dentine simple in structure ; the exter- 
nal surface is formed by a layer of smooth and polished enamel. 
The body of Onychodus was covered with imbricated scales, nearly cir- 
cular in outline, and about an inch in diameter. The under surface of the 
scale is marked by fine concentric lines, as in Holoptychius. The exposed 
portion of the outer surface is ornamented with a tuberculation not unlike 
that of the plates, consisting of radiating but broken lines, and confused 
groups of minute, furrowed, appressed cones. 
This genus was established by the writer many years ago to receive 
certain conical, curved teeth found in considerable numbers in the Cornif- 
