364 S. W. WILLISTON 
observed by the writer, those of the present specimen on their 
free surface show numerous, irregularly placed, minute pits leading 
into nutrient canals. 
The ribs, for the most part, are preserved in position. Each 
has a rather prominent and stout tubercle lying in apposition 
with the end of a diapophysis; and the capitulum lies in the inter- 
central space below the middle of the vertebra, and near the end 
of the very slender intercentrum. The fractured ends of the ribs 
show a small central cavity filled with crystals. 
The block of matrix, as discovered, showed along its fractured 
edges, nearly parallel with the under side of the vertebrae, two 
series of overlapping, slender, 
bony lines, which were first 
supposed to be merely imbri- 
cated ventral ribs, though the 
absence of fractured ends was 
inexplicable. When the lateral 
surfaces were cleared of matrix 
these lines were found to be the 
fractured edges of bony plates. 
Fic. 1—Ostodolepis brevispinatus Wil- These lines lie along the broken 
liston. Posterior dorsal vertebrae from edge of the block in very orderly 
the side and in front, with articulated are 8 
Le rece eee arrangement, their inner, pos- 
terior ends about one millimeter 
apart; they are directed obliquely forward and cutward. Each 
line measures about eight millimeters in length, and is of about the 
thickness of writing paper; they lie closely upon each other and are 
straight. The external, anterior, and very thin margins of these 
scutes are directed forward, a remarkable arrangement. None of 
the scutes can be laid bare completely, but the numerous ones seen 
on the surface below the vertebrae show a width of each approxi- 
mating its length. The angles are broadly rounded. ‘The outer 
surface seems to show shallow concentric grooves, possibly corres- 
ponding to the free margins of the overlying scutes, of which there 
are about six. Under a hand lens they show very distinct, slender 
raised lines, quite concentric with the free margin. In general the 
scutes resemble the cycloidal scales of bony fishes. 
