MONOGRAPH OF JAPANESE OPHIUJiOIDEA. 85 



more or less stumpy and usually have spiny tips. Interradial 

 ■ventral surfaces strongly concave, each with two large, nearly 

 parallel genital slits. A single madreporic shield is present at the 

 inner border of an interbracliial ventral surface. Teeth and dental 

 papillae similar, spiniform, forming clusters at the apices of jaws. 

 Oral papillae absent, so that the sides of the oral slits are naked. 

 Arms simple, covered by a pavement of gi-anules, distinctly an- 

 nulated by zones of densely set, minute, compound hooks, each of 

 which consists of one main and several supplementary booklets. 

 Three to five arm spines, peg-like, usually with rough tips, serving 

 as tentacle scales. 



This genus includes Astrotoma hellator Kœhler, 1904, vecors 

 Kœhler, 1904, and rigens Kœhlee, 1910, besides the genotype, 

 Astrothamnus echinaceus. They may be distinguished as follows. 



Key to species of Astrothatnnus. 



A — Brachial ventral surfaces smooth ; spaces just inside the interbrachial 

 ventral surfaces, as Avell as oral angles, beset with slender spines ; 

 three arm spines. 



« — Basal arm spines unusually long and stout, longer than the cor- 

 responding arm joints rigens, 



aa — Basal arm spines not unusually long and stout, nearly as long as 



the corresponding arm joints vecors. 



A A — Brachial ventral surfaces, spaces just inside the interbrachial ventral 

 surfaces, as well as oral angles, beset with coarse, stumpy granules. 

 h — Three arm spines not very small, nearly as long as the correspond- 

 ing arm joints echinaceus. 



bb — Five arm spines Aery small, hardly half as long as the correspond- 

 ing arm joints bellator. 



The distribution of Astrothamnus is very interesting, for, as 



