134 



K. M1TSUKUK1. 



would be necessary to modify the last part of the generic definition as 

 follows: "Integument with numerous wheels, sometimes also with 

 dichotomously branched bodies." 



The same point also separates off the present species at once from 

 I. maculatus, Theel, the only species, so far as I can discover, known 

 hitherto of the genus. 



The main features of the species are as follows : — 

 Body elongated, of almost equal breadth throughout, being in 

 largest alcoholic specimens 120-1 60 mm. long and 35-40 mm. wide, about 

 3-4 times as long as broad. Mouth anterior, subventral. Anus 

 posterior, subdorsal. Tentacles fifteen, with large circular discoidal 

 ends ; on the whole, the ventral tentacles smaller than the dorsal. The 

 odd ventral ambulacrum naked. Pedicels of each lateral ambulacrum 

 22-25, the alternate arrangement of pedicels in the inner and outer rows 

 of each amlulacrun very obvious in some specimens, and hardly 

 recognizable in others, the difference being probably due to the degree 

 of contraction in alcoholic specimens. Processes of each of the dorsal 

 amlulacra very numerous, conical, rather short, the longest about 

 one-third of the width of the body, in about four rows, of which the 

 inner two are sometimes distinctly separated by a space from the outer 

 two. Back naked in the median dorsal interamlulacrum, with the 

 exception of the genital process in the anterior part. Integument soft, 

 sometimes thin, sometimes thicker and spongy (the difference being 

 probably due to the state of preservation), more or less translucent, most 

 so in fresh state, internal organs (especially light-colored organs like the 

 generative organs) being visible from the surface. Calcareous deposits 

 of two kinds ; large wheels with six central rods and small wheels 

 mostly with four central rods. Among the former, the largest are about 

 0.21 mm. in diameter and have about nine spokes (See ThÉel, loc. cit. 

 pl. XXX VI, fig. 15). These grade off intolthose about 0.1 mm. in diameter 

 and with about twelve spokes. Various stages of growth in the large 

 wheels are visible, as given by Theel. The small wheels (See Theel 

 loc. cit. pl. XXXVI, fig. 17) are 0.046-0.059 mm. in diameter. In them 



