MONOGRAPH OF JAPANESE OPHIUROIDEA. 243 



about as long as the width of the correspondmg lateral arm plates. 

 There are three or four of them for each lateral plate. 



With the exception of the peripheral zone, the ventral surface 

 of the interradial spaces of the pentagonal body is covered by a 

 thin skin, which contains fine, close-set, polygonal or rounded, 

 delicate, transparent scales. The peritoneal cavity and the genital 

 glands can be seen through the skin, and apparently extend into 

 the arm bases. The genital bursse are absent and the genital 

 openings are invisible. There is only one oral shield, the mad- 

 reporite, which is irregularly triangular, and so transparent and 

 small as to be almost invisible unless the specimen is dried, and 

 distinguishable only with difficulty from the scales of the inter- 

 brachial ventral surface, and is moreover separated from the 

 adorai shields by a space. The adorai shields are long and very 

 narrow, tapered within to a point, outer end joined to the first 

 ventral arm plate, inner end free, longer than the first ventral 

 plate. Oral plates large and stout, oblong quadrangular, with 

 exceedingly short inner side, convex abradial and concave or 

 nearly straight adradial side, much wider without than within, 

 joined distally to the first ventral arm plate and proximally to 

 each other along the proximal one-third of the abradial side. A 

 single dental plate is present in each jaw, quadrangular in ventral 

 view with curved inner edge. There are six or seven papillae to 

 each jaw, arranged in a horizontal, continuous row, situated deep 

 within the oral slits, and directed not laterally but upwards. The 

 two or three apical ones arise from the dental plate, so that they 

 may be regarded as dental papillae, while the outer papilla3 he 

 just below the first oral tentacle pores and protect the latter, so 

 that they may possibly be the tentacle scales of the same. 



Ventral arm plates eight or nine in number, limited to within 



