142 PALEOZVIC FISHES OF NORTH AMERICA, 
plate varies considerably in the different species; being quadrangular in D. 
Terrelli and D. intermedius, more rounded in D. Gouldii and D. minor. 
The suprascapulas are oblong and closely resemble in all things but 
size those of Coccosteus. Their upper margins are overlapped by the dorsal 
plate, while the lower margin is covered by the bifurcated expansion of the 
clavicles. These latter have never before been figured, though good speci- 
mens have been in my possession for several years. One of a complete 
pair is represented, one-third natural size, by inside and outside views on 
1b GN AQUE 
Internal bones belonging to the shoulder girdle have been found in 
many instances. ‘These I have provisionally called coracoids, but I am by 
no means sure of their proper relations. They are sometimes a foot and a 
half in length, somewhat curved, subeylindrical at one end and in the mid- 
dle, expanded and flattened at the other; are nearly as large as one’s arm, 
and consist of dense bony tissue. 
On Pl. VI is figured a triangular bone with which I have long been 
familiar, but Lam not yet able to fix with certainty its position on the body. 
It is sometimes an inch in thickness at the center and the largest specimens 
are nearly a foot and a half in length. Only the central portion was ex- 
posed, the ends and curved margin being deeply marked by the impressions 
of overlying plates. A short furrow belonging to the lateral line system 
passes from what was apparently the upper side to about the center of the 
exposed portion and there vanishes. The straight or nearly straight edge 
is rounded, shows no indications of contact with other plates, and was 
evidently free. Two places have suggested themselves as possible for this 
plate: one behind and overlapped by the suborbital plate, in that case 
forming the continuation of the upper margin of the mouth; another and 
more probable place was in the angle between the lateral margin of the 
dorsal plate and the posterior margin of the suprascapula. From the con- 
dyle on the anterior margin of the latter plate a furrow runs obliquely 
backward to the posterior margin and would seem to have been continued 
on some adjacent plate. A similar triangular plate occupies this position 
in Coccosteus, and waiting the time when it shall be found in its normal place, 
we may provisionally fix it here. 
