of the ^^ Genus " Peneus. 513 



Trachypeneus is found, on the one hand, in the West 

 Indies and neighbouring coasts of America, and, on the 

 othei' hand, in Oriental seas from India to Japan. 



Atypopeneus is known with certainty only from the Bay of 

 Bengal, but it probably occurs also in the China Sea. 



Key to the Genera of the Maniple Peneus. 



I. Roati'Lim serrated both on its dorsal aud on its 



ventral edge ; a pleurobranch on the last tho- 

 racic somite (XIV.) ; exopodites on all or all 

 but the last pair of the thoracic legs. 



1. First pair of chelipeds short Peneus (s. r.), 



2. The first pair of chelipeds of the male are, 



typically, stouter and vastly longer than the 



second and third pairs Heteropeneus. 



II. Rostrum serrated on its dorsal edsre only. 



1. A pleurobranch on somite XIII. but not on 



somite XIV. 

 i. Exopodites on all or all but the last pair of 



the thoracic legs Metapeneus. 



ii. The thoracic legs have no exopodites Purapeneus (s. r.). 



2. No pleurobranchise on somites XIII. and X LV. ; 



all the thoracic legs with exopodites. 

 i. Epipodites wanting from at least the last 



thi'ee pairs of thoracic legs Parapeneopsis. 



ii. Epipodites absent from only the last two 

 pairs of legs. 



a. Last two pairs of legs of normal form. 



A. Antennular flagella short Trachypeneus. 



B. Antennular flagella much longer than 



the carapace Atypopeneus. 



b. Last two pairs of legs extremely long and 



slender (flageUiform) Xiptiopeneus. 



III. Diagnoses of the constituent Genera and Tables 

 OF THE Species of the several Genera. 



1. Peneus, Fabr. (sensu restricto). 

 Peneus, Fabr., Sidney I. Smith, Proc. U.S. Nat. Mus. viii. 1885, p. 170. 



Type, P. caramote, Risso. 



Rostrum toothed both dorsally and ventrally. Antero- 

 inferior angles of carapace not spiniform. Postantennular 

 sulcus of carapace defined by a dorsal as well as a ventral 

 ridge. 



Antennular flagella short or of moderate length. Endo- 

 podite of maxillules (first maxillae) elongate and distinctly 

 3-jointed. Exopodites present on all or all but the last pair 

 of the thoracic legs. 



Ann. (^ Mag. N. Hist. Ser. 7. Vol. xvi. 31 



