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



accompaniments are developed as effectively as in the most highly-organised apparatus 

 of any genus in the families of the Noemalia. 



It appears, therefore, taking into consideration the external features in connection 

 with the branchial characters, that the following is the natural classification : — 



Group ABERRANTIA. 



Pereion short, posterior somite loosely articulated with the preceding ; pleon long, somites increasing in 

 size posteriorly, not overlapping each other dorsally ; first pair of pereipoda more or less imperfectly chelate ; 

 posterior pair short, more or less ahnormal ; branchiaa variable in number and form. 



Division I. 

 Family Galatbeidje. 

 Pereion broad and dorsally depressed ; carapace anteriorly produced into a rostrum ; first pair of antennas with 

 flagella short second pair without a scaphocerite ; second pair of gnathopoda pediform ; first pair of pereiopoda 

 chelate, subequal ; second, third, and fourth simple, robust; posterior pair enfeebled; pleon broad and 

 depressed ; somites short and slightly overlapping each other ; rhipidura equilateral and foliaceous. In develop- 

 ment the brephalus takes the form of a zcea. Genera Galathea, Munida, Grimothea. 



This family will be reported on by Prof. J. R. Henderson, M.B., F.L.S., in another volume of this series. 



Division 1 1. 



Family PylocbelidjE. 



First pair of antennae with flagella short ; second pair with scaphocerite ; first pair of pereiopoda chelate, 

 symmetrical ; rhipidura rigid ; telson transversely divided ; branchiae filamentous, in two rows, cylindrical ; 

 mastigobranchi;e and podobranehiae wanting. Genera Cheiroplatea, Pomatochdes, Pylocheles. 



Family Tiiai.assinid.e. 



First pair of pereiopoda subchelate, unequal ; branchiae filamentous and foliaceous ; rhipidura rigid ; 

 mastigobranchiae and podobranehiae rudimentary. Genus Thalassina. 



Family Calliaxassid.e. 



First pair of antenna; with flagella long, second without a scaphocerite ; first pair of pereiopoda asym- 

 metrical, unequal ; rhipidura foliaceous ; branchiae filamentous, compressed. 



(A) Podobranehiae and mastigobranchiae wanting ; second pair of pleopoda unlike the third and following 



pairs. Genera Cdllianassa, Cheramus, Scdllasis, Trypxa. 



(B) Podobranchiae wanting ; mastigobranchiae present ; second pair of pleopoda like the following pairs. 



Genus Oallianidea. 



(C) First pair of pereiopoda subchelate; rhipidura foliaceous; branchiae like Callianassa; second pair of 



pleopoda like the following pairs. Genus Gebia. 



Family Axiid.e. 



First pair of pereiopoda chelate, subsymmetrical, unequal ; branchiae filamentous, cylindrical, and com- 

 pressed ; podobranchiae and mastigobranchiae present. Genera Axius, Paraxms, Mconasdns. 



