HOLOTHURIOIDEA OF THE INDIAN OCEAN. 75 



External Characters. — There is a distinct separation of the 

 bivium from the trivium, the latter bearing pedicels only, 

 and the former papillae. The general ground colour of the 

 spirit specimens is grayish-yellow. The pedicels, which do 

 not show any arrangement into rows, are brown-coloured with 

 yellow sucking discs. Each pedicel is surrounded by a white 

 ring. On the bivium the papillae are situated on the summits 

 of warts of various sizes, the largest being arranged in two 

 rather irregular rows near the middle of the back. There are 

 about six in each row, and each of these is surrounded by 

 a broad bluish-black area, which joins with the dark area 

 around the corresponding papillae of the other row to form a 

 transverse band. There are about six of these bands. In 

 some cases the dark area in question is separated from the 

 papilla by a light ring, as described by Augustin (1). The 

 smaller papillae are arranged irregularly, although there is a 

 shght suggestion of an arrangement into rows, especially near 

 the junction of the bivium and trivium. Most of these small 

 papillae are dark-coloured and are surrounded by a light ring. 

 The tentacles were not seen in any of the specimens. 



Internal Structure. — -The calcareous ring is typical of the 

 genus. There is a single stone canal on the right side of the 

 dorsal mesentery, and there is a single Polian vesicle. The 

 left respiratory tree is larger than the right, and Cuvierian 

 organs arise from the base of the left respiratory tree. In the 

 specimens examined the gonads were well developed and 

 extended to the posterior end of the body. 



Spicules. — The calcareous deposits consist of tables and 

 buttons. The tables have a disc 40 \^ in diameter, generally 

 consisting of four larger central holes and alternating with 

 these four smaller peripheral holes. The spire is generally 

 imperfectly formed and has no definite shape. It may consist 

 of three or four uprights which do not join at their summit, or 

 there may be two irregular uprights diverging towards the 

 summit, where they are connected by an irregular cross beam. 

 These tables are hardly to be distinguished from those of H. 

 curiosa. The buttons consist of a central axis, from which are 

 given off from three to six irregular outgrowths at each side, 

 and are about 20 JJ- in length. They remind one strongly of 



