CRUSTACEA. 
193 
Mesothyra spum^a, n. sp. 
PLATE XXXII, FIGS. 8, 9 ; ANJ> PLATE XXXIV, FIG. 2. 
Two specimens, one displaying the ventral aspect of the caudal plate and 
the lateral spines, the other, a single long caudal spine, show the following 
points of difference from either of the species Mesothyra Neptuni or M. Oceani: 
the caudal plate is broader and its postero-lateral margins straight; the cer- 
copods are broad and flat and taper very slowly, their outer margin being 
thickened or carinate, and the inner bearing an inconspicuous ridge; the sur¬ 
face of the test is smooth or very finely granulose, with a few pustules and 
elevated strim on the spines near the lines of articulation. The cercopods are 
broader and stouter than in M. Oceani and very much smaller than in M. Neptuni. 
In surface ornament it differs from either. 
Distribution. Hamilton group. From the dark shales at Pratt’s Falls and 
Delphi, Onondaga county. 
Mesothyra (Dithyrocaris ?) Veneris, n. sp. 
PLATE XXXIII, FIG. 3. 
Cephalothorax. Right valve only known; this is longitudinally semi-ovate, 
widest anteriorly, and more than twice as long as wide. 
Dorsal line straight along the median portion of the valve, bending gently 
outward toward the anterior extremity for the formation of the rostral cleft. 
Just within, and parallel to the dorsal line, is a finely impressed line, which 
runs from the posterior extremity of the carapace about two-thirds the 
length of the shield, to a point analogous in position to the strong angle 
observable on the hinge in the species Mesothyra Oceani (q. v.), where it 
merges into the dorsal line. Were this narrow strip along the dorsum, which 
is included between the hinge-line and this linear furrow, removed, the out¬ 
line of the dorsal margin would be the same as in that species. This feature 
has an important bearing upon the interpretation of the character of the 
dorsal articulation in M. Oceani. 
The anterior extremity appears to be produced at the dorsal line into a 
short spine continuous with the carapace. The specimen is slightly fractured 
