KEPORT ON THE HOLOTHURIOIDEA. 123 



which are seen in Irpa, Dan. and Kor., and Kolga, Dan. and Kor. Special attention 

 should be paid to the peculiarity that the C-curved bodies which are found in Stichopus, 

 Brandt, as well as in the Elasipoda always present a significant dilation at their middle. The 

 branched spicules seem to be present in the majority of the deep-water forms, and may be 

 considered as especially characteristic of the two families Elpidiidse and Psychropotidse ; 

 they are made up of four or sometimes three more or less spinose and arcuate arms, and 

 are supplied either with only a single outwardly-directed spinose central process or with 

 several such, which give to the surface of the body-wall a high degree of roughness. It is 

 very surprising to find the wheel-shaped deposits represented in several forms of Elasipoda, 

 for these calcareous bodies have always been considered as characteristic of only a few 

 genera of the apodal Holothurids, viz., Myriotrochus, Steenstrup, Chirodota, Eschscholtz, 

 Trochoderma, Theel, and Acanthotrochits Dan. and Kor. Two kinds of wheels are dis- 

 tinguishable, viz., large or true wheels and small ones resembling plates, the former 

 of which seem to be never present unless associated with the latter as is the case in 

 Lcetmogone, Ilyodcemon, and Pannychia, while the latter, on the contrary, seem to be 

 more independent of the presence of the former, and are sometimes found together with 

 spicules (PI. XXXII. figs. 21-23, and PI. XXXIII. fig. 6), as in Achlyonice lactea, 

 Elpidia ambigiia, &c. I do not intend to give any detafled account of the structure 

 of the wheels, but refer back to the description of the species. I only intend to draw 

 attention to the fact that the regularly large nave has in its centre a large hole, from the 

 edge of which an inwardly-directed crown, made up of four to five arcuated arms, rises. 

 I have observed, especially in Pannychia and Ilyodcemon, that this central hole is 

 sometimes covered with a thin, transparent calcareous membrane pierced by a few some- 

 times minute openings (PI. XXXII. fig. 6), the centre of this calcareous membrane being 

 connected with the top of the crown by a short, straight, calcareous rod. 



The plates which are present in Deima and Oneirophanta are of a different structure ; 

 those which belong to the former genus are composed, that is to say made up of several 

 layers (PL XXXI. figs. 5 and 11), while the plates in the latter genus are simple, dis- 

 coidal, and flat. The simple as well as the compound plates vary considerably in size, 

 the larger being mingled with the smaller ones ; the largest plates I have seen in 

 Oneirophanta measure about 2 or 3 mm. in diameter, while those in Deima fastosum, 

 attain to 5 mm., and in Deima validum to about 7 mm. diameter. The simple plates 

 are perforated by numerous holes, which are always largest at the centre and diminish 

 gradually towards the circumference, where they become almost indistinguishable ; the 

 innermost layer of the compound plates resembles the simple ones in the fact that the 

 perforation is more regular and the rather rounded holes decrease towards the circum- 

 ference, and upon the upper surface of this inner plate, or rather layer, rises a more 

 irregular network, which in Deima fastosum appears like a large conical knob (PI. XXXI. 

 fig. 10), while in Deima validum it does not attain such a development, but only gives 



