8 AET. 2. — H. MATSUMOTO : 



very thick. Oral frames either long and slender or short and 

 very stout, without well developed lateral wings. Arms slender, 

 not exceedingly long, always simple. Dorsal arm plates absent or 

 rudimentary, lateral arm plates subventral in position, so that the 

 dorsal side of the arms is mostly unprotected. Arm spines not 

 confined to the ventral side, skin-covered. Vertebrsß rather slender, 

 not very short and discoidal, often incompletely calcified and more 

 or less divided into halves by a longitudinal, fusiform pore. 

 Vertebral articulation zygospondyline, the articular peg being well 

 developed, or streptospondyline, the peg being very rudimentary or 

 entirely absent. Both upper and lower muscular fossae large. 



This family includes twenty-two genera, which may be grouped 

 into two subfamilies as follows : 



Subfamily 1. Ophiomyxince mihi, 1915. — Oral sliields small, 

 separated from the first lateral arm plates by the outer lobes of 

 the long and slender adorai shields ; vertebra long and very 

 slender, often divided into halves ; wings of the vertebrae very 

 much thinner laterally than dorsally, so that the vertebrae are 

 fairly rhomboidal in dorsal view ; vertebral articulation zygospon- 

 dyline, the articular peg being well developed. 



I. Second oral tentacle pores opening outside the oral slits. 

 a. Teeth present, arranged in a single vertical row. 



Ophiohelus Lyman, 1880. 



Ophiosciasma Lyman, 1878. 



Ophiogeron Lyman, 1878. 



Astro ger on Verrill, 1899. 



Ophlostyracium Clark, 1911. 



Opliiooynodus Clark, 1911. 

 h. Teeth almost absent. 



Ophiosyzygus Clark, 1911. 



