SUPER-ORDER V MALACOSTRACA 667 
Bittner, are known from the Eocene and Oligocene. The recent Thelphusa, 

Fic. 1024. 
Xanthopsis Kressenbergensis, v. Meyer. Eocene; Kressenberg, Bavaria. Male, ventral and dorsal aspects, 1/2. 
Latr., and Gecarcinus, Leach, occur in the fresh-water Miocene beds of Oeningen 

Fic. 1403. Fia. 1404. 
Xanthopsis Bruckmanni, v. Meyer. Eocene ; Sonthofen, Coeloma vigil, M.-Edw. Eocene; Laverda, 
Bavaria. Ventral view of female, 1/;. Italy. 
and Engelwies in Baden. Archacoplax, Stimpson, is found in the Miocene of Gay 
Head, Massachusetts. 
Order 5. HDRIOPHTHALMA. Leach. 
(Arthrostraca, Burmeister ; Tetradecapoda, Dana.) 
Malacostraca with lateral sessile eyes, usually with seven, more rarely six or fewer free 
cephalothoracic segments, and an equal'number of pairs of legs adapted for creeping or 
swimming. 
Sessile-eyed Crustacea are somewhat rare in the fossil state, and as a rule are 
imperfectly preserved ; this, taken in connection with the fact that the classification is 
largely based upon the minute mouth-parts, makes the identification and systematic 
arrangement very difficult and often impossible. 
