CRUSTACEA. 193 



Mesothyra spumjEA, n. sp. 



PLATE XXXII, PIGS. 8, 9; an,. 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 Hat 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 strioe 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. Plight 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 



