1896. ] NEW YORK ACADEMY OF SCIENCES. 239 
Size.—Length of pygidium, 3 mm.; width, 4 mm.; the head- 
shield is somewhat shorter. 
Horizon and Locality.—Limestone of the Olenellus Zone at 
Troy, N. Y. Collected by Mr. C. Schuchert and communicated 
to the author. 
Though this species is not of the Paradoxides Zone, I have 
described and figured it here on account of its resemblance to 
the larval stages of certain Microdisci of that zone. It differs 
from others with which it occurs in its short glabella and broad, 
depressed head shield; in these points it is like M. Dawsoni. 
While the typical species of the Olenellus Zone have retained 
the occipital ring, it appears to be wanting or nearly effaced in 
this species, as in several species of the Paradoxides Zone, and in 
the Agnosti. The larval pygidia of the Eodisci (I. pulchellus, 
etc.) resemble the adult shield of this species in contour, num- 
ber of rings in the rachis, etc. And it is to a fixed larval stage 
of this type, rather than to MM. pulchellus, M. punctatus or M. 
Dawsoni that the author would look as the source of such a 
form as M. connexus, Walc.; for this species differs little from . 
M. Schucherti, except in the extension of the occipital spine. 
All our examples of M. Schucherti show only the outer surface, 
and so it is not known whether the border fold of the head shield 
is crenulated within. 
MIcCRODISCUS PRECURSOR. Plate xvii., fig. T. 
Microdiscus punctatus var. precursor, Trans. Roy. Soc. Can., 
vol. ili.,.pts lv.,/p. 1o,,pl.. vil., fig..13. 
Only the head shield of this species is with certainty known. 
It resembles M. pulchellus, but is more triangular in outline. 
The marginal rim is very narrow; the dorsal furrow is deep and 
wide and connected with the marginal furrow by a shallower 
furrow. Glabella shows two faint pairs of furrows at the sides, 
Microdiscus precursor, supposed pygidium mag. 4°. (This figure should 
have been placed between figs. 4b and 8d on Plate xvii. ) 
on the inside of the test, smooth on the outside. The occipital 
ring bears a tubercle or short spine. The cheeks are tumid, 
nearly straight on the side next the dorsal furrow, to which they 
descend abruptly; at the posterior inner corner is a prominence 
which projects toward the glabella in front of the occipital ring. 
