144 AKT, 2. H. MATSUMOTO : 



shield. Peristomial plates entire, or rarely double, nsnally very 

 small. Oral frames very stout, with strongly developed lateral 

 wings as a rule, for the attachment of voluminous masticatory 

 muscles. Oral and dental plates usually very stout, the two plates 

 usually presenting an X- shape in dorsal view. Oral papillae few, 

 often entirely absent. Dental papillaa well developed only in forms 

 without oral papillae. Teeth stout, usually quadrangular, with 

 widened, straight or wavy apical edge. Arms slender, inserted 

 ventrally to the disk, horizontally flexible, or sometimes more or 

 less coiled vertically. Vertebral articulation zygospondyline. 

 Dorsal, lateral and ventral arm plates all well developed. 



Key to families of GnatJiophiurida. 



A — Teeth triangular, not very stout ; peristomial plates large ; oral 

 frames entire, without well developed lateral wings ; genital plates 

 free, not fixed to the basal vertebrae ; oral papillse present ; no dental 



papillae AmpliilepididcB. 



AA — Teeth quadrangular, very stout ; peristomial plates small ; oral frames 

 with well developed lateral wings ; genital plates firmly fixed to the 

 basal vertebrae. 



a — Oral papiUse present ; no vertical clump of dental papiUae 



, AmpJiiuridœ. 



aa — Oral papillae absent ; dental papillae weU developed, forming a 

 vertical clump at the apex of each jaw Ophiotrichîdœ. 



Family 1. Amphilepididae Matsumoto, 1915. 



Disk covered with fine, imbricating scales. Radial sliields 

 Bometimes very rudimentary but often well developed, with a 



