858 THE VOYAGE OF H.M.S. CHALLENGER. 



merit of some of the pereiopoda, while others are well formed ; for instance in the genus 

 Pasiphsea the first two pairs of pereiopoda are well developed, whereas the three posterior 

 pairs are diminutive in size and imperfectly formed. 



The genus Leptochela has also the first two pairs of pereiopoda well developed, while 

 the three posterior pairs are slender and feeble. In Pasiphsea there is no synaphipod 

 attached to the mandibles, and in Leptochela the same appendage is only single-jointed. 

 In Orphania the chelate pereiopoda are well developed, and the three posterior slender 

 and feeble. 



These three genera I propose to unite in this one family, and there are probably others 

 which may be found possessing features that may bring them within its range. 



Leptochela, Stimpson. 

 Leptochela, Stimpson, Proc. Acad. Nat. Sci. Philad., p. Ill, 1860. 



Carapace smooth, scarcely crested ; lateral walls and margin destitute of spines. 

 Rostrum very short, spiniform. 



First pair of antennae biflagellate. 



Mandibles inflexed, broad, and compressed ; synaphipod short, ovate, and uniarticulate. 



First pair of gnathopoda not pediform, having the last joint armed with long spines. 



Second pair of gnathopoda furnished with an ecphysis. 



Pereiopoda carrying a basecphysis. First and second pairs compressed, chelate, 

 slender, with long parallel dactyli ; three posterior pairs short. 



Pleon having the antepenultimate somite more or less abruptly curved. 



Pleopoda biramose, rhipidura well developed. 



Telson long, narrow, and tapering. 



The above definition corresponds closely with Dr. Stimpson's description of the 

 genus, which he considers to bear a close affinity to Pasiphsea, differing only in having 

 the mandibles with a synaphipod, and in the first pair of gnathopoda not being pediform. 



The description coincides with the characters of the specimen in the Challenger 

 collection, except that what Dr. Simpson calls "long spines" on the terminal joint of 

 the first pair of gnathopoda I should have called hairs. 



The arrangement of the branchiae, as observed in Leptochela robusta, is shown in the 



following table : — ■ 



Pleurobranchiae, . . . 1 1 1 1 1 



Arthrobranehiae, . . . 1 1 1 1 



Podobranclrias, . . . 



Mastigobranohioe, . . . r r 



h i k 1 m n o 



Geographical Distribution. — Dr. Stimpson obtained some specimens of Leptochela 

 gracilis from deep water in the Gulf of Kagosima, and Leptochela robusta, at a depth 



