MONOGRAPH OF JAPANESE OPHIÜROIDEA. 233 



either outside or inside the oral shts ; arms short and stout, stoutest 



at the base OpMolepididœ. 



act — Disk covered with granules ; second oral tentacle pores opening 

 always within the oral shts; arms moderately or very long. 

 b — Arms slender, inserted ventrally to the disk, stoutest at the base or 



at a distance from it ; arm spines few OpJiioîeucidœ. 



lb — Arms stout, inserted laterally to the disk, stoutest at the base ; arm 



spines numerous OpJiiodcrmalidce, pars. 



AA — Arm spines long and erect. 

 c — Dental papillae absent. 



d — Disk covered with granules ; oral angles granulated ; arms stout, 



stoutest at the base ; arm spines numerous .... 0}dModermatidœ, pars. 



dd — Disk usually free of granules ; oral angles not granulated ; arms 



slender, stoutest at a distance from the base ; arm spines few .... 



OphiocMtonidce. 



cc — -Dental papillae well developed, forming a vertical clump at the apes 

 of each jaw ; arms stout, stoutest at a distance from the base .... 

 Opliiocomidœ. 



Family 1. Ophiolepididae Ljungman, 1867. 



Disk covered with thick scales or plates, among which the 

 primaries are often very prominent. Radial shields usually stout. 

 The radial shield and genital plate on the same side of a radius 

 articulate with each other by means of two articular condyles and 

 one articular pit on both the plates. Genital papillae very often, 

 and arm combs sometimes, present. Oral papillœ usually few, 

 arranged in a single series ; where the second oral tentacle pore 

 opens within the oral slit, the outermost oral papilla is pointed 

 inwards and the next one is the largest. Teeth arranged in a 

 single vertical row. Dental papillœ absent. Peristomial plates 

 small, usually double, rarely simple. Arms inserted laterally to 



