236 ABT. 2. — H. MATSÜMOTO : 



Oph iocer amis Lyivian, 1865. 



The internal structures of the Ophiomastinœ are very divergent, 

 but roughly three types may be distinguished according to the charac- 

 ter of the peristomial plates. The first type, represented by Astro- 

 phiura and Ophioplinthus, lacks the peristomial plates ; the second, 

 represented by Ophiomastus and Opliioden, has simple peristomial 

 plates ; and the third, including the majority of the present sub- 

 family, has double peristomial plates. 



The internal structures observed in Astrophiura kawamurai are 

 most peculiar. The oral frames and plates are very long and 

 slender, while the dental plates are stout. The peristomial plates 

 are entirely absent, though the peritoneal membranes of the oral 

 region, as well as of the other parts, contain very fine, trans- 

 lucent, perforated scales, much resembling the perforated spicules 

 of holothurians, as seen under a compound microscope. The 

 genital plates and scales are entirely internal, both being very 

 slender and narrow ; the former are very short, with the outer end 

 forming a simple articular face for the radial shield ; the latter 

 are about twice as long as the former, parallel to, and directed 

 above, the adorai shields, not laterally but terminally articulated 

 with the genital plates. The proximal parts of the first lateral 

 arm plate curve inwards and downwards, passing below the radial 

 shield and the genital plate, and articulate with the first vertebra. 

 The dorsal side of each vertebra is not rhomboidal but almost 

 quadrangular, with a rather shallow median groove ; that of the 

 first vertebra is much wider than in the others, the abradial 

 peripheries being very thin and translucent. The ventral side of 

 each vertebra has a rather shallow median groove and a well 

 marked median suture. The vertebra3 of the free arms are almost 

 entirely divided into halves by a very narrow moniliform slit, the 



