P I N A C A R I D yE . 
MESOTHYRA* n. g. 
MeSOTHYRA OcEANI, 11 . sp. 
PLATK XXXII, FIGS. 1-0; PLATE XXXIII, FIGS. 4-7; and PLATE XXXIV, FIGS. 1-5. 
Dithyrocaris Neptuni, Hall. Illustrations of Devonian Fossils, pi. xxii, figs. 1-.5 ; pi. xxiii, figs. 1-3. 1876. 
Dithyrocaris Neptuni, Etheridge, Woodward and Jones. Fifth Rept. Committee on Fossil Phyllopoda of 
the PaliEOzoic Rocks. 1887. 
Cephalothorax sub-quadrate or broadly spatulate; length to width as 2.5 to 1. 
Surface flattened along the axial region, slightly convex and normally some¬ 
what deflected on the sides. 
The dorsal line is nearly straight for three-fourths its length from the poste¬ 
rior extremity; thence bending inward and again curving outward it makes 
a broad, conspicuous angle opposite the eye-node; passing thence forward to 
the anterior extremity, forming the margin of the rostral cleft, and intersect¬ 
ing the anterior margin of the valve at an acute and slightly incurved angle. 
The angular extension upon the dorsal line is of the same length on both 
anterior and posterior slopes. On the anterior extremity of the carapace the 
margin is transverse for a short distance, rounding in a constantly widening 
curve along the ventral edge to very near the posterior extremity; thence 
backward it is slightly incurved, and at the postero-ventral angle is con¬ 
tinued as the margin of a strong, sharp spine, which is directed inward. 
The posterior margin is transverse and nearly straight, terminating at the 
dorsal line in a short, sharp, posteriorly directed angle. On the anterior and 
* The distinctive featui-es upon which the type species of this genus (D. Oceani) is separated from the genus 
Dithyrocaris have not been noticed in any of the descriptions oi* illustrations of species of that genus given 
by English or Amei-ican authors. The interpretation of the chai-acters of the carapace, as here given, 
requires the removal of these forms from the family Cbratiocaridje, and if the described sjiecies of 
Dithyrocaris shall, upon reexamination, prove to possess similar features, they may all be united under the 
family name proposed above. 
