186 SPOLTA ZBYLANICA. 



arranged than the former and are evenly scattered over the 

 ventral surface without showing, as a rule, any disposition into 

 rows. In a young specimen about 100 mm. long, however, 

 I have discerned three rows of tube feet, each row being about 

 eight pedicels wide. 



Internal Structure. — The calcareous ring differs but Httle 

 from the usual type seen in this genus. The radials have 

 three anterior concavities, the middle one being shallower 

 than the two lateral ones. The inter -radial piece has a single 

 anterior tooth. 



This species has a variable number of stone canals. In 

 various specimens I have counted from six to twenty, equally 

 disposed on both sides of the dorsal mesentery. The stone 

 canals generally have a twisted stalk and a swollen end, and 

 sometimes they are branched. Selenka (22) in his account 

 mentions the presence of a " knoplformig " stone canal and then 

 proceeds to mention the presence of " eine anzahl von kleinen 

 mit elliptischen korpern prall gefiillten Blaschen." Whether 

 these bodies are really stone canals as their position in his 

 figure would suggest, and whether they are similar to the 

 bodies described by me from Actinopyga serratidens, I cannot 

 say. The number of Polian vesicles is also variable. In the 

 specimen with twenty stone canals there were three long 

 narrow Polian vesicles 30 mm. long in the contracted condition. 

 Frequently only one vesicle is present. 



Spicules. — The deposits are very characteristic, and are of 

 two distinct kinds. Those on the bivium are either small 

 dichotomously branching " rosettes " 50 f. long, or longer 

 spinous rods 80 [x in length. The deposits of the ventral 

 surface consist entirely of oval grains 22 i^ in diameter. 



General Remarks. — There appears to be some reason for 

 Theel's suggestion that Actinopyga agassizi is probably a 

 variety of the above species. The two, however, differ with 

 regard to the spicules of the bivium. In A. agassizi they 

 consist of small X-shaped bodies, which are not so numerous 

 as the characteristic spiny rods of A. mauritiana. The cal- 

 careous rings are similar, and in both cases there are about 

 twenty-five tentacles. In a specimen of A. agassizi examined 

 by me, the body had a uniform colour of chocolate -brown with 



