66 ART. 2. — H. MATSUMOTO : 



small and narrow, being narrower than the first vertebra and the 

 basal free vertebrae of the arms, and are covered over by the 

 muscles lying between them and the genital plates. The genital 

 plates are very stout, lying close on the sides of the adjacent ver- 

 tebra?. The genital scales are very small, articulated to the outer 

 parts of the genital plates. The radial shields are long, narrow, 

 thick, with humped interior surfaces, nearly reaching the disk 

 centre. The gastral cavity is divided into ten radiating pouches, 

 the roof being firmly attached to the body wall. The floor of the 

 gastral cavity has ten attachments, the radial ones extending from 

 the second vertebra to the disk margin and the interradial ones 

 from the peristomial plate to the same. The perihaemal canal 

 commuicates with the genital bursœ, which are very spacious. 

 The peritoneal cavity is perfectly divided into five radial compart- 

 ments, which are entirely filled up by the generative glands. The 

 ventral arm plates are rhomboidal, much wider than long, separated 

 from one another by the lateral arm plates, which meet each other 

 in the ventral median line. The abradial parts of the lateral plates 

 strongly project ventrally to form a very prominent spine ridge. 

 The minute hooks of the annuli of the arms are compound, being 

 composed of a terminal main booklet and of three to five comb- 

 like supplementary ones. In Astrotoma sobrina, the essential 

 structure is almost similar, but the supplementary plates in the 

 spaces between the oral angles and the interbrachial ventral sur- 

 faces are better developed ; the muscles lying between the basal 

 vertebrae and the genital plates are more massive ; the radial 

 shields are distinctly keeled ventrally ; the radial attachments of 

 the floor of the gastral cavity extend from the first vertebra? to 

 the disk border ; and the minute hooks of the annuli of the arms 

 are composed of from one to three supplementary booklets, besides 



