94 ART. 2. H. MATSÜMOTO : 



V. Radial shields long, narrow, bar-like. 



Ophiacantha Müüler à Tröschel, 1842. 



Ophialcœa Verrill, 1899. 



Ophiacanthella Verrill, 1899. 



Ophiolebes Lyman, 1878. 

 VI. Radial shields large, long, wide. 



OpJdothamnus Lyman, 1860 (— OplHoleda Kœhler, 

 1906). 



Ophiurothamnus, nov. 



Ophiomytis Kœhler, 1904. 



Ophioplinthaca Verrill, 1899. 



Ophiomitra Lyman, 1869. 



Ophiocamnx Lyman, 1878. 

 As the present family includes both those forms with only 

 horizontally flexible arms and those with more or less coiled arms, 

 two types of internal structures are also distinguishable roughly. 

 The first type, found in those forms with only horizontally flexible 

 arms, is characterised by the very thin, delicate, sometimes divided 

 peristomial plates, the slender oral plates and frames, the very 

 slender vertebrae, the very thin wings of the basal vertebrae, the 

 more or less divided distal vertebrae and the zygospondyline vertebral 

 articulation. The second type, found in those with more or less 

 coiled arms, is characterised by the very thick, always entire 

 peristomial plates, the more or less stout oral plates and frames, 

 the more or less short, stout, always entire vertebne, the more or 

 less thick wings of the basal vertebrae and the usually strepto- 

 spondyline vertebral articulation. l^he internal structures of 

 Ophiothamnus venustiis Matsumoto is almost perfectly similar to 

 those of 0. vlcarius Lyman. The peristomial plates are very large, 

 thin and triple, the two paired secondary plates forming an out- 



