MONOGRAPH OF JAPANESE OPHIDROIDEÄ. 95 



wardly open angle, which is occupied by the unpaired median 

 one. The oral plates and frames are short and slender. The 

 genital plates are long, more or less club-shaped, lying closely 

 parallel in pairs, just above the arm base. The genital scales 

 are absent. The genital bursas ate very rudimentary, being 

 represented merely by the creases between the interbrachial 

 ventral surfaces and the arm bases. The generative glands are 

 enclosed in a membranous sac, the waU of which contains fine, 

 thin, transparent scales, when viewed under the microscope, just 

 as is stated by Moeïensen to be the case in Ophiopus arcticus. 

 The vertebrae are very slender, and those of the distal arm joints 

 are imperfectly divided into halves by a series of pores, just as 

 in Mlcrophlura according to Mortensen. The last named genus 

 is stated to lack the genital plates and scales and to have entire 

 or divided peristomial plates, besides an additional plate, which is 

 perforated by a pore just between the peristomial plates and the 

 oral shield. I imagine that, the perforated plate just referred to 

 may correspond to the unpaired secondary plate of the peristomial 

 system, because I know that in certain genera the unpaired 

 secondary plate has a half pore on its outer border. In OphioUmna 

 antarctlca (Lyman) and 0. papillata (Clark), the peristomial plates 

 are large, wide, short, thin, imperfectly divided, with soldered 

 halves, the oral plates and frames are short and slender, and the 

 genital plates and scales and genital bursae are normal. In 

 Opliiolocjimus hcxactis Clark, the internal structures are essentially 

 similar to those of OphioUmna, which has also imperfectly 

 divided peristomial plates. The radial ' shields though externally 

 invisible, are present and short and rounded. Also in this species 

 I was able to prove that the distal vertebrae are imperfectly 

 divided by a series of pores. According to Lyman, Ophiomyces 



