194 
PALEONTOLOGY OF NEW YORK. 
at this point so that only the outline of the spine can be detected. As it 
occupies the position of the rostral plate, there may be room for question 
whether this is not such a body, but with the present evidence, all indica¬ 
tions are that it is a prorate spine coalesced with the carapace and thus 
necessarily existing on each valve. Below this spine the margin slopes 
rapidly backward to the ventral edge, along which, for a short distance, it is 
nearly parallel to the dorsal line. The valve narrows backward, and at the 
posterior extremity the margin is produced into an acute and slightly in¬ 
curved spine, between which and the dorsal line the outline is strongly 
incurved. The margin is very slightly elevated and appears to be broadly 
infolded in the postero-ventral region, as in M. Oceani, the posterior spine 
being a prolongation of this infolded margin or doublure. 
The Surface is smooth, slightly and evenly convex. The cephalic region 
bears an optic node distant from the dorsal line, and in its vicinity the cara¬ 
pace has apparently been somewhat compressed over some irregularity in the 
matrix. On the thoracic region is a faint longitudinal ridge, nearly parallel 
to the dorsal line, which becomes obsolete toward the posterior extremity. 
Dimensions. The single valve measures 38 mm. in length, inclusive of the 
anterior and posterior spines, and 16 mm. in its greatest width. 
Distribution. Hamilton group. In the Marcellus shales, on Mud Creek, East 
Bloomfield, Ontario county. 
Dithyrocaris Belli. 
Bithyrocarifs Belli, Woodward. Geol. Magazine, p. 106, pi. iii, fig. 5. 1871. 
Dithyrocaris Belli, Etheridge, Woodward and Jones. Fifth Rept. Committee on Fossil Phyllopoda of the 
PaliEOzoic Rocks, p. 6. 1887. 
This species was described from an extremely imperfect specimen in which 
the valves of the carapace apparently overlap along their inner margins, only 
their anterior portion being retained. The drawing shows two strong carinse, 
but gives no indication of the hinge-line. The anterior extremity bears a short 
spinule similar to that in the species Mesothyra {Dithyrocaris ?) Veneris, and the 
surface is ornamented by abundant striae. 
Distribution. Middle Devonian. Gaspe, Province of Quebec. 
