PI N AC ARI I) .]•: 



MESOTHYRA,* n. g. 

 Mesothyra Oceani, n. sp. 



I'L \TK XXXII, FIGS 1-0; PLATE XXXIII, FIGS. 4-7; AND PLATE XXXIV, FIGS. 1-5. 



Dithyrocarls Neptuni, Hall. Illustrations of Devonian Fossils, pi. xxii, figs. 1-5; pi. xxiii, tig's. 1-3. 1S76. 

 Ditkyrocaris Neptwii, Etheridge, Woodward and Johes. Fifth Rept. Committee on Fossil Phyllopoda of 



the Palaeozoic 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 features upon which the type species of this genus (D. Oceani) is separated from the genus 

 Ditkyrocaris have not been noticed in any of the descriptions or illustrations of species of that genus given 

 by English or American authors. The interpretation of the characters of the carapace, as here given, 

 requires the removal of these forms from the family Ceratiocarid;e, and if the described species of 

 Ditkyrocaris shall, upon reexamination, prove to possess similar features, they may all be united under the 

 family name proposed above. 



