DESCRIPTION OF SPECIES 323 



that the outline of the compound eyes and a few other features of the 

 dorsal surface are visible from the ventral side. 



Description : Body small ; ovate-lanceolate in outline ; entire length, 2 

 inches ; greatest width about one-third of the distance from the anterior 

 end, where it measured 9 /i 6 of an inch. 



Carapace a little more than one-fifth of the total length of the body; 

 subrectangular in outline; length, y 2 inch; width, 7 /™ inch; lateral mar- 

 gins nearly straight, anterior margin gently convex-forward; antero- 

 lateral, angles rounded; posterior margin nearly straight except at the 

 genal angles, where it curves slightly forward. Compound eyes mod- 

 erately large, nearly one-third the length of the carapace, situated in front 

 of the middle, more than twice as far apart as distant from the lateral 

 margins, reniform, prominent; ocelli not visible. Ventral surface of 

 carapace much broken. 



Preabdomen about one-sixth the length of the body, wider than long, 

 greatest width about the fourth segment ; the edges of the ventral plates 

 project slightly beyond the dorsal, which are slightly produced back-' 

 ward into short spines. Postabdomen a little more than one-third the 

 length of the body, the width decreasing more rapidly in the first and 

 second postabdominal segments than in the more posterior ones; the 

 length of the segments progressively increasing posteriorly; post-lateral 

 angles slightly produced into short spines. 



Telson about one-fourth the length of the body, rapidly contracting 

 from the articulation into a slender spiniform process, which tapers to 

 a mucronate point, and is carinate on the ventral side. 



Appendages indistinct; imperfect impressions of portions of the proxi- 

 mal parts of three appendages are visible on each side of the carapace, 

 but are too indistinct to permit of description. 



Horizon and locality: In the lower part of the Essex (Edgewood) lime- 

 stone ; near Essex, in Kankakee County, Illinois. 



Explanation op Plates 

 Plate 15. — Mayville limestone 



Figure 1. — View of the Mayville limestone. 



The limestone overlies the iron ore in Iron Ridge, near Neda, 

 Wisconsin. 



Figure 2. — Quarry in the Mayville limestone. 



The quarry is half a mile south of Peebles, Wisconsin. The 

 upper layers furnish fossils characteristic of the Edgewood 

 formation. 



XXIV— Bull. Ghol. Soc. Am., Vol, 27, 1915 



