352 The American Geologist. December, 1903. 
Pectoral tins very large and strong, 8 inches long by 5^ in greatest 
width at base. The}' expand 22 inches Erom tip to tip, the fore margin 
is 13 Va inches behind the tip of the snout. 
The teeth are as in the generic description on a somewhat forking 
base, they are slightly striate. 
Mono clad odus pinnatus Claypole. 
This was a somewhat larger fish than the preceding species, measur- 
ing from tip to tip of the pectoral fins 24 inches. In general so far as 
is yet known the species differs little from the preceding, but its pecul- 
iar character lies in the great strength of the ventral fins which in all 
the previously mentioned forms were too weak to be distinctly marked 
in the fossil. Here they nearly equal the pectorals in strength though 
not in size and contain 12 strong bony rays. 
Further details regarding this and other fossils from the same shale 
may be found in the pages of the American Geologist for the years 
189^, 1894, and 1895. 
it is scarcely necessary to point out the fact that the pres- 
ence of these sharks in the waters of the Appalachian gulf im- 
plies the presence of other fishes suitable for their food. This 
condition could hardly have been fulfilled by the great placo- 
derms, Dinichthys, etc. In the stomach of one of Dr. Clark's 
specimens lies the half digested and macerated relics of a small 
Callignathus whose jaws are yet distinguishable. Other sim- 
ilar indications may be seen on some of the other specimens. 
The great armour-plated fishes have passed away and 
have left but few and small representatives of their family 
in our present seas. But the smaller and unarmed, but active 
sharks are still abundant and are in many places the dominant 
fishes of the ocean. It may not be out of place to ask, Why is 
this so ? 
Nature probably had her time of experiment with armour- 
plating. She loaded bony protection upon these Devonian 
fishes until the limit of possibility was almost or quite attained. 
In some specimens of Dinichthys the supraoccipital bone is 3 
inches thick. Secured thus against most of their dnemies, 
these ponderous creatures must have been slow of motion. It 
is also probable that their hinder parts were unprotected. No 
trace has been found of any covering. Possibly in spite of their 
enormous size and weighty plating they were open to attack 
by their enemies from behind and could not escape by flight 
or turn and destroy their small but nimble assailants, whose 
agility rendered them formidable for attack and safe in retreat. 
