64 STALK-EYED CRUSTACEA. 
readily distinguished from the latter by the great size of the right cheliped, 
the irregularly oval outline of the right chela, the great length of the distal 
segment of the antennular peduncle, etc. 
Pylopagurus affinis Fax. 
Plate XII, Fig. 2-2. 
Bull. Mus. Comp. Zodl., XXIV. 169, 1893. 
This species is nearly related to P. wngulatus, from which it differs in the 
following respects : the eye-stalks are longer, and narrower at the distal end ; 
the external prolongation of the second segment of the antenna is longer 
and slenderer ; the upper margin of the carpus of the right cheliped is armed 
with two or three spines, the largest of which is close to the anterior border ; 
the outer face of the carpus is smooth save where a light tubercular ridge 
runs along the middle. In P. ungulatus this face of the carpus is thickly 
covered with spinulous granules which assume larger proportions and a uni- 
serial arrangement on the superior and inferior margins. On extending the 
comparison to the large chela, further differences between the two species 
become apparent. In both species the external face is flat, covered with 
minute spinulous granules, and surrounded by a border of sharp spines ; but 
in P. affinis the marginal spines are larger and more irregular, and the flat 
opercular facet is not sharply defined at the proximal end by the regular 
arrangement of the marginal spines as in P. wngulatus ; instead, one finds the 
marginal series of spines broken down at this point, thus effacing any distinct 
limit between the opercular face of the chela and the articular surface which 
connects the propodite with the carpus. The inner or lower surface of the 
large chela is smooth in P. affixis, granulated in P. wigulatus. The left cheli- 
ped is quite different in the two species: in P. affinis the several segments of 
which it is composed give rise to long sete which give the appendage a 
very hairy appearance when contrasted with P. wngulatus ; the inferior 
border of the chela is conspicuously toothed, while in P. ungulatus it is entire. 
The ambulatory legs are more hairy in the Pacific species than in P. wngu- 
latus, and their carpal joints are not so distinctly dentate on the superior 
border. The rasps of the fourth pair of legs are multiserial in both species. 
The telson P. affnis is symmetrical, subcircular in outline, its posterior border 
convex and entire ; in P. wngulatus, the telson has a deep and wide posterior 
median notch. 
