28 ART. 2. — H. MATSUMOTO: 



and ventral arm plates, as well as the skin- covered arm spines, 

 confined to the ventral side of the arm. Vertebra) very short and 

 exceedingly stout, discoidal, with typically streptospondyline arti- 

 culation. Upper muscular fossas of the vertebras extremely large, 

 the lower very small. 



This family includes ten genera, which may be grouped into 

 three subfamilies as follows : 



Subfamily 1, Asteronychînœ mihi, 1916. — Disk large and arms 

 slender ; only a single madreporite is present ; perihsemal canal 

 entirely closed ; peritoneal cavity divided into five separate com- 

 partments by the interradial attachments of the gastral pouches to 

 the body wall ; genital bursas free from the perih^emal canal, but 

 communicating with each other in radial pairs ; lateral arm plates 

 of either side separated from each other by the comparatively 

 large ventral arm plates ; more than three arm spines on each 

 plate. 



Astrodia Veeeill, 1899. 



Aster onyx Müllek & Teoschel, 1842. 

 Subfamily 2. TricJiasterince mihi, 1915. — Disk moderately 

 large and arms moderately stout ; one madreporite to each inter- 

 radius ; perihsemal canal and genital bursas with open communica- 

 tions ; lateral arm plates of either side separated from each other 

 by the ventral arm plates, distal ones projecting ventrally in the 

 form of hanging rods ; two subequal arm spines on each plate. 

 I. Arms simple. 



Ophiuropsis Studee, 1884. 



Astroceras Lyman, 1879. 

 II. Arms divided. 



Trichaster Agassiz, 1835. 



SthenocephaÏKS Kœhlee, 1898. 



