CRUSTACEA— MALACOSTRAC A. 393 



gills, features not preserved in the fossil forms known. They will 

 hence be included under the older genus. Cambarus is living today 

 east of the Rocky Mountains, and Astactis (Potamobius) on the 

 west side, and in Europe. 



39. A. (Cambarus?) primaevus Packard. Eocenic. 

 Similar to the modern C. affinis Say, with a similar long narrow 



pointed rostrum; first pair of thoracic legs shorter and stouter 

 than in the living form, and chelae rather shorter ; surface of 

 carapace, post-abdomen, and legs coarsely tuberculated ; telson and 

 broad rami of last pair of pleopoda spined as in living species of 

 Cambarus. 



Green River beds of Wyoming. 



40. A. subgrundialis Cope. Pliocenic. 

 Surface of cephalothorax smooth or obsoletely wrinkled ; two 



tubercles on each side of rostrum, which is narrow, medially 

 grooved and acute, with five spinous points on each side, and a 

 terminal recurved spinelet ; chelae not granulate, superior edge spini- 

 ferous; margins of segments of post-abdomen produced into acumi- 

 nate plates. 



Fresh-water Pliocenic of Idaho. 



Suborder Brachiura Latreille. 



Body flattened, round oval, triangular or quadrangular, generally 

 transverse, never much elongated. Regions of the cephalothorax 

 generally strongly outlined; sternum mostly well-developed, often 

 showing seven-partite character. Abdomen reduced, without caudal 

 fin, and bent round on ventral side ; in the male it is narrow and 

 pointed, with one to two pairs of abdominal feet; in the female 

 it is broad with four pairs. Anterior thoracic legs alone furnished 

 with chelae in the typical divisions; antennae short, sometimes not 

 visible from above. The principal external characters are shown 

 in the accompanying figure of a recent crab (Fig. 1694). 



Ortmann restricts the Brachiura so as to include only the super- 

 families Oxyrhyncha or triangular crabs, Cyclometopa or bow 

 crabs, and Catometopa or quadrangular crabs. The Oxystomata 

 or round crabs, and the Ranioidea and Dromiacea he separates 

 and places into distinct divisions of equal rank with the Brachiura, 

 the first two under Oxystoinata, and the last under Dromiidce. 



