DEVONIAN FAUNAS. 337 
series of truncated cones arranged one above the other, and are not 
unlike the casts of 7. elongatus which occur in both earher Helder- 
bergian faunas and in the Oriskany, but the specimens are smaller 
than the typical 7. elongatus, the largest specimen observed having a 
maximum diameter of 2 mm. 
Tentaculites acula was originally described from the ‘Lower Hel- 
derberg Group, Port Jervis, Orange county,” but the particular 
stratum from which the specimens were secured is not mentioned. 
The species probably came from the “trilobite bed,” however, as all 
the new species which have been described as coming from the 
Helderbergian series of Port Jervis are, so far as can be determined, 
from this bed. The larger specimens which have come under obser- 
vation are much larger than those which Hall described, although 
many individuals may be found of the size of that figured by Hall. 
The smaller specimens agree with Hall’s brief description in having 
regular, equidistant annuli, but the few annular striz on the intervals 
cannot be detected on the casts. In the larger individuals the an- 
nulations become somewhat more irregular. 
CEPHALOPODA. 
ORTHOCERAS sp. undetermined. 
Plate XLIIIL., Figs. 16-17. 
The only Cephalopods detected in the “trilobite fauna” are frag- 
ments of one or two species of Orthoceras too imperfect for identifi- 
cation. The largest specimen observed (fig. 16) is a shell 22 mm. 
in diameter, with sutures about 4 mm. apart. The septa are rather 
deeply-concave and the sipuncle is situated centrally. The shell 
itself is wholly destroyed, so that the nature of the surface-markings 
cannot be determined. Another smaller specimen is apparently a 
fragment of the chamber of habitation of an Orthoceras, as no sutures 
are present. It has a diameter of about 8 mm. and seems to be marked 
by fine, transverse lines of growth. 
22 
