46 PROCEEDINGS OF THE ACADEMY OF [Feb., 



Order I. PHRYNOPHIURIDA nov. 



Disk and arms covered by a skin. The radial shield and genital 

 plate articulate by means of a simple face or a transverse ridge on 

 either plate, without well -developed articular condyles and sockets. 

 Peristomal plates large, entire, or sometimes double or triple. Oral 

 frames entire, without well-cleveloped lateral wings. Dorsal arm 

 plates absent or very rudimentary; lateral arm plates ventral or 

 sub ventral in position; dorsal side of arms largely unprotected. 



Key to families of Phrynoiphiurida. 



yl— Lateral arm plates more or less subventral; arm spines not 

 confined to ventral side of arm, but lateral or subventral in 

 position; vertebrae not very short and stout, with not exceed- 

 ingly stout wings; upper and lower muscular fossae of vertebrae 

 rather subequal; radial shields smaU or rudimentary, 



Ophiomyxid.e. 

 A A — Lateral arm plates and arm spines confined to the ventral 

 side of the arm; vertebrae very short and stout, discoidal, 

 with exceedingly stout wings; upper muscular fossae of 

 vertebrae extremely large, lower very small; vertebral articu- 

 lation typically streptospondyline; radial shields long and 

 bar-like. 

 a — Arms without rows of hook-bearing granules; arm spines 

 covered by thick skin; adoral shields very stout, 



Trichasterid^. 



aa— Arms annulated by double rows of hook-bearing granules; 



arm spines naked, or at most covered by thin skin; adoral 



shields rather small and inconspicuous, often separated 



from oral shields by small supplementary plates, 



Gorgonocephalid^. 



Family 1. OPHIOMYXIDuE Ljungman, 1866. 

 (Characters as given above in key.) 



Key to subfamilies of Ophiomyxidce. 



A — Oral shields separated from first lateral arm plates by outer 

 lobes of the adoral shields; peristomal plates usually double 

 or triple, not very thick, not firmly fixed to the oral frames, 

 which are rather slender; vertebrae long and slender, except 

 one or two basal ones which are discoidal, distal ones usually 

 divided into halves; wings of vertebrae not equally thick, 

 but distinctly much thinner laterally than dorsally; vertebral 

 articulation zygospondyline, the articular peg being well 

 developed Ophiomyxin^e. 



A A — Oral shields in contact with first lateral arm plates; adoral 

 shields entirely proximal to oral shield; peristomal plates 



