MONOGRAPH OP JAPANESE OPHIUROIDEA. 57 



lies the naked genital plate, which is large, oval, and tuberculous 

 under the microscope like the radial shields. Thus, each inter- 

 bracliial ventral surface is bounded on either side by the genital 

 plate. Oral angles puffed laterally, almost fiUing up the' oral shts. 

 Teeth small, triangular, arranged in a single vertical row. No oral 

 or dental papilla?. 



Arms very wide at the base, keeping the same width to the 

 distance of about 4 or 5 mm., then rather rapidly narrowed, be- 

 coming slender and cylindrical, with the width of about 1 mm. ; 

 covered with scales similar to those of the disk. Arm joiuts in- 

 visible in the proximal part, but more or less distinct distally. 

 First tentacle pore without arm spine, the following ones with one 

 spine, which is very small, short, peg-hke, somewhat flattened, 

 rough at the end under the microscope, lying flat on the ventral 

 surface of the arm. Half way out in the arms, the tentacle pores 

 are each provided with two spines, of which the second or the 

 abradial one is exceedingly small and rather inconspicuous ; while 

 the adradial one is a little longer and erect. 



Colour in alcohol white or light pale yellow. 

 In smaller specimens, the arms are scarcely widened at the 

 base, which is also the case in regenerating ones ; for, schizogony 

 takes place in this species, as in the genotype, A. virgo KœiTlek. 

 Most specimens are five-armed, but the arms are often unequal, 

 two or three being larger than the others. I have, however, one 

 specimen with six arms, three larger and three smaUer. In the 

 four-armed specimens, two or three of the arms may be larger 

 and the other two or one smaller. Still another specimen has 

 only three arms and three pairs of radial shields, doubtless in- 

 dicating that it has lately undergone division, and that the lost 

 parts have not been regenerated. It can be easily observed in 



