222 TRANSACTIONS OF THE [May 18 
trifissus. A head 33 mm. shows three fore-furrows of the gla- 
bella as A. trifissus, but no axial furrow of the glabella. 
A pygidium 4mm. long, is wide, subquadrate, marginal fur- 
row distinct, not widened ; fold widened, cuspidate, rachis promi- 
nent, front lobe divided off by a shallow furrow, second lobe de- 
fined only by the axial tubercle, third lobe not defined, weak, 
rapidly descending below the cheek lobes, which are wide be- 
hind the rachis. A pygidium 1} mm. long, is quadrate; the 
third lobe from the front is defined, but the little tubercle is ab- 
sent. Another common variety is the following : 
Var. TRUNCATUS 0. var. ? 
2? Agnostus truncatus Brogg. Om. Paradoxides skifrene ved 
Krekling, p. 72, tab. vi., fig. 8. 
Brégger’s figure, except that it is somewhat more quadrate 
and larger, is not distinguishable from a common variety of A. 
parvifrons that occurs in the St. John group. The variety 
found here does not differ from var. tessella, except that the 
front lobe of the glabella is entirely suppressed, and that the 
individuals are found of larger size. 
Size.—Length and width of each shield, 4 mm. 
Horizon and Locality.—As the preceding. 
Considering these varying forms, we are impressed with the 
justice of Tullberg’s remark that this is a variable species. In 
Agnostus Acadicus of Hartt we may perhaps have an ancestral 
form of this species ; that occurs in the sub-zone of Paradoxides 
Eteminicus; then in the sub-zone of P. Abenacus we find three 
other forms, var. declivis of A. Acadicus, in which the front lobe 
begins to be depressed, var. fessella of A. parvifrons, in which 
the front lobe is traced out on the surface of the head-shield only 
by an impressed line, and not by furrows, and var. truncatus, in 
which the front lobe entirely disappears; finally, one may add 
the typical form of A. parvifrons, in which any suggestion of 
an anterior lobe is removed by the rounding of the front of the 
glabella. It will be noted that there is a resemblance in the 
pygidia of all these forms, and that A. Acadicus differs from 
the typical Fallaces in the absence of marginal spines to the 
pygidium, a feature which it possesses in common with all 
parvifrontes. 
AGNOSTUS UMBO, pl. Xvi., figs. 4a and b. 
Agnostus umbo. Trans. Roy. Soc. Can. vol. iii., pt. iv., p. 
Tl, pl. vii., figs. 8a and b. 
Body elliptical, broader in front than behind, high at the inner 
side of the head and tail shields, descending thence to the front 
