308 BULLETIN" 93, UNITED STATES NATIONAL MUSEUM. 



The maxilla has three large spines and a group of small ones 

 above the rather deep notch (fig. 87/;). 



Cirrus i has rami of 8 and 6 segments, the posterior ramus three- 

 fourths the length of the anterior. The posterior border of the 

 basal segments of the anterior ramus bears some very short, stout, 

 slightly curved spines, much as figured for C. cirratus^ but not noticed 

 in any other species. 



Cirrus ii has rami of 6 segments, the posterior ramus shorter by 

 the length of one segment. The terminal segments of both rami 

 have several simply serrate spines and a few broad ones with two 

 coarse teeth below the finely serrate portion, as shown in figuj-e 87c'. 



Cirrus iii has rami of 12 segments; cirrus iv of 14 and 15 segments; 

 cirri v and vi of 16 segments. The segments of these cirri have three 

 pairs of spines (fig. 87fZ). 



Chthamalus challengeri differs from stellatus by the well developed 

 adductor ridge of the scutum. The articular ridge is shorter than in 

 C. stdJ-atus and differs in shape, its greatest prominence being near 

 or above the middle of the tergal margin, with lower end tapering, 

 not terminated abruptly as in stellatus. Some forms still referred 

 by authors to stellatus have a tergnm resembling that of challengerL 



The description and figures 1, 1« of plate 72 represent the valves 

 of a Matsushima specimen. Figure 3 is a group from Yokohama 

 growing on Tetraclita s. japonica, borne by a living Ilelcioniscus 

 eucosmius. The largest in this group reach 6 mm. in diameter. 



Specimens from Ayukawa, Japan (pi. 72, figs. 2, 2a), have some 

 small crests crossing the lateral depressor pit in some specimens^ 

 others having it simple. There is the slight rudiment of a spur on 

 the tergum. The mandible is like that of typical stellatus. Maxilla 

 as figured for challengeri. Cirrus ii has rami of 5 segments, the 

 terminal segments having dense groups of spines, none of them 

 pectinate. The posterior cirri have four pairs of spines. Cirrus vi 

 Avith 13 segments (fig. 87e). A^liether these peculiarities of the cirri 

 have racial significance remains to be investigated. 



Specimens collected in Japan by Mr. Loomis, seated on Balanus 

 cariosus, are corroded, with rather short valves, the adductor ridge 

 of the scutum strong but very short, pit for the lateral depressor 

 muscles well marked (pi. 72, figs. 4, ^a). Exterior white. 



Doctor Kriiger has figured two Japanese forms of CTitKanfnalus. 

 According to his account there are no differences in the mouth 

 parts, and the scuta of both are figured with an adductor ridge. I am 

 therefore disposed to suggest that the form he calls C. stellatus is 

 more closely related to challengeri than to the Atlantic species, wliich 

 has no adductor ridge. 



