200 
Tetraf/raptus qiiadribrachidtiis, Pritchard (non J. Hall), Proc. Roy. 
Soc. Yict., H.S. YII., 1895, p. 30. 
Tetragraptus decipiens, T. S. Hall, The Graptolites of the Lance- 
field Beds, Yictorian Graptolites, pt. II., ibid XI., 1899, p. 168, pi. 
XYII. & XYIII. 
Tetragraptus decipiens, T. S. Hall, Reports on Graptolites. Rec. 
Geol. Surv. Yict., vol. II., pt. I., pp. 2 & 3; vol. III., pt. 2, pp. 191-7, 
199-200, 202-4, 206-7. 
Description. —The lon¬ 
gest nema (virgula) ob¬ 
served, about 5 mm. in 
length, is thin and filiform. 
Sicula, rarely seen in toto, 
about 2'3 mm. long. The 
first thecse apparently or¬ 
iginates within apical third 
of sicula, and the first two 
thecse on each side of the 
sicula,form the stipe of the 
first order, which, together 
are from 2'5 to 3‘5 mm. 
long and 7 mm. wide. 
r-■... 
X. 
•// 
v/ 
4 
V,' ~ 
. / 
\ \'>v 
Fig. 64. —tetragraptus decipiens, T. S. Hall. 
Obverse aspect of polvpaiT showing nema x3i. Geol. Surv. 
Coll. No. 240. 
Stipes of the second order are approximately straight, of an ob¬ 
served length of over 35 mm., but probably longer, gradually widening 
from .6 mm. proximally to 1.5 mm. distally. In some specimens a 
thickening of the dorsal wall of the coenoisarcal canal is evident (pi. 
XXXIY., fig. 1a). 
Thecae 9 to 11 in 10 m., narrow, from four to six times as long as 
wide, slightly curved, inclined about 34° proximally and 27° distally, 
overlapping for about half their length. Apertural margins of proxi¬ 
mal thecae about normal to the direction of the stripe, straight or 
slightly concave; those of distal thecse normal to axis of thecae, concave. 
Remarks. —Dr. HalPs original description^ was as follows:—‘‘ From 
stout branches arising close to' the sicula, apparently from the second 
and third thecae and from 0.5 to 1 mm, broad. Thecae slightly expand¬ 
ing, overlapping for about one-half their length; apertural margin 
concave, set at an angle of 95° to 100° to axis of branch; on the margin 
with a slight concave curvature which gently increases near the aper¬ 
ture; inclined first at an angle of 10° to the branch and near the aper¬ 
ture of about 30°. Yirgula shown as a fine line, often about 7 mm. in 
length.’’ 
Affinities. — T. decipiens is undoubtedly allied to T. quadrihrachiatus, 
but is probably more closely related to Glonograptus, the common an¬ 
cestor of the Dichograptids. The simple tubular thecee of T. decipiens 
are illustrated by pi. XXXIY., fig. 1a, and are more suggestive of 
Clonograjjtus than T. quadrihrachiatus. 
1 T. S. Hall. Proc. Roy. Soc. Vict. XI., 1899. 
