of the Pacific Shores of North America. 503 



PAL^MON HETEKOCHIRUS. Wiegmann. 

 Palaemon heterochirus, Wiegmann; Archiv fur Nalurgeschichte, 1836, i. 149. 



This is another of the large fresh-water shrimps of 

 Mexico. They frequently attain a length of two feet, in- 

 cluding that of the chelopoda, which are at least as long as 

 the body. 



Mus. Berlin. 



STOMAPODA. 



SQUILLA DESAUSSUREI. Stimpson. 

 Squilla scabricauda, Desaussure, (non Latr.) Rev. et Mag. de ZoOl. v. 367. 



Hab. Mazatlan, (Verreaux.) 

 Mus. of M. Verreaux, Paris. 



ISOPODA. 



IDOT^A CONSOLIDATA. Stimpson. 

 Idotrea consolidata, Stimpson ; Proc. Col. Acad. Nat. Sci. i. 89. 



Body convex, broadest at the fourth thoracic segment. 

 First four segments of thorax larger in every dimension 

 than the last three, each bearing an umbo near the lateral 

 margin, which is turned up a little. A sharp, slightly 

 elevated transverse ridge across the thorax on each segment 

 near its posterior margin. No distinct epimeral sutures. 

 Abdomen convex, formed of a single piece, with a slight 

 transverse impressed line, indicating the partial separation 

 of an anterior segment ; it is narrowed toward the posterior 

 extremity, which is terminated by a slight concavity. Head 

 emarginate at the middle in front ; cephalic suture distinct, 

 separating a small segment from the posterior part of the 

 head ; eyes strongly convex, laterally projecting ; a promi- 

 nent minute tubercle just in front of each eye. External 

 antennae half as long as the body ; nagellum with ten 



