No. 380.] DEVONIAN PTYCTODONTIDE. 551 
on the anterior margin being 20 cm. The width where it is 
broken off below, which is not far distant from the beginning 
of the exserted portion, is 5.5 cm., and the maximum thickness 
at this point is 5.5 mm. The spine 
is extremely compressed laterally, both 
sides being almost flat. There is no 
strongly marked anterior keel. The 
posterior face is slightly sulcated, and 
each side of the sulcus is set with 
Closely approximated tubercles of 
somewhat larger size than those oc- 
curring elsewhere. The bottom of 
the sulcus is traversed by a faint lon- 
gitudinal ridge, triangular in section. 
The individual stamp imparted to 
this spine by its flattened, arcuate 
shape is heightened by its peculiar 
ornamentation. The lateral faces are @ 
beset with numerous small tubercles i 
ing a tendency to become parallel to 
the anterior and posterior margins. 
One of Mr. Monroe’s spines has the 
tubercles disposed more numerously 
along a series of parallel grooves, 
Situated some distance apart, the 
whole presenting a more or less con- 
centric appearance, and indicating 
successive growth stages in the de- 
velopment of the organ. The appear- aha 
ances indicate that the inserted por- Fic. 49.—Phlyctenacanthus telleri 
tion tapered gradually toward the i td parea fe u a 
base, but this region itself has not 
been recognized on any of the specimens thus far examined. 
Most of the tubercles have been worn down smooth to their 
bases, or are evenly rounded on top, but a few retain traces 
of a fine original stellation. One or two spines, instead of 
