1896. | NEW YORK ACADEMY OF SCIENCES. 221 
Test smooth. Head-shield enclosed by a marginal fold that 
is broader in front. Glabella small, round, not lobed. Basal 
lobes small. Cheeks expanded, connected in front of the gla- 
bella; pygidium without spines; marginal fold wider behind ; 
rachis long, almost reaching the border; lobes sometimes obso- 
lete, sometimes apparent; middle joint ornamented with an 
elevated point; lateral lobes narrowed behind, scarcely con- 
tiguous. 
Size.—Length and breadth of each shield, 35-44 mm. 
Horizon and Locality.—Dark gray shales of Div. 1d! at 
Porter’s Brook, St. Martin’s, etc. 
Mr. C. D. Walcott has described a species of Agnostus of the 
parvifrons type found in the Lower Cambrian rocks of Wash- 
ington County, N. Y. Being claimed as a Lower Cambrian (7. 
é., Olenellus Zone) fossil, it is not figured here. The glabella is 
longer than in A. parvifrons. It may be remarked, however, 
that this type of Agnostus is not found elsewhere lower down 
than the P. Abenacus (=tessini) sub-zone. 
A common variety in Canada is the following : 
Var TESSELLA. pl. xvi., figs. a to c. 
Agnostus tessella. Trans. Roy. Soc. Can. vol. iii., pt. iv., p. 
(1, pl. vil., figs. Ta to.c. 
This is a transitional form to the Limbati (Fallaces). It dif- 
fers from the type in having an anterior lobe to the glabella 
faintly defined ; this has no furrow like the posterior lobe, but 
is marked out by a faint thread-like line on the surface of the 
test. The posterior lobe is intermediate in length between the 
two glabellas of A. parvifrons figured by Tullberg, but rect- 
angular in front. The pygidium is similar to fig. 27) of Tull- 
berg’s plate, but the tubercle is elongated, not round as in that 
form; the rachis is wider, and its middle lobe proportionately 
shorter. The marginal fold does not have so great a width be- 
hind. 
Size.—Length and width of the shields each 3 mm. 
Horizon and Locality.—Same as the preceding. 
Development of the Young.—A head shield 4 mm. long is nar- 
row, marginal fold and furrow distinct. Glabella long, front fur- 
row distinct, two others faintly marked by depressions crossing 
the glabella; basal lobes very narrow, scarcely visible.* 
A head 14 mm. has nearly the form of the adult, slight fur- 
rows at the anterior corners of the glabella as in A. /issus var. 
: *This is in accordance with the changes of this lobe in the Ptychoparide in which 
during the first larval satges this somite is very narrow and weak. 
