47c 



NATURE 



\_March 18, 1880 



could succeed in hearing with it, but all with whom the 

 experiment was successful preferred the card audiphone 

 to that of ebonite. 



A number of deaf mutes under the care of M. Sager, 

 were blindfolded and provided with audiphones ; the 

 distances from a grand piano, at which they began to 

 hear the sounds, indicated their different degrees of 

 deafness. They could distinguish at once between the 

 high and the low notes of the instrument, and between its 

 tones and those of a violoncello. The shrillest tones of 

 the violin produced little effect. Similar experiments 

 were made by M. Colladon in another establishment for 

 deaf-mutes, near Geneva, under the care of M. Forestier. 



Mr. Thomas Fletcher, of Warrington, has communi- 

 cated to us a further improvement. After a long series of 

 experiments he has found the best material of which the 

 audiphone can be made is birch-wood veneer. If cut to 

 an oval about 12 inches by 8 J, and steamed and bent to a 

 curve, it does not require the cords of the Rhodes' pattern, 

 and is more convenient for use than Colladon' s form. 

 Mr. Fletcher states that a disk of half the above size 

 suffices for a musician who may, in consequence of partial 

 deafness, require such aid, and who cannot use a hearing 

 trumpet on account of the inconvenience of holding it 

 while playing his instrument. The disk of veneer is so 

 light that it may be held between the teeth without effort 

 and almost without consciousness of its presence. If 

 •stained black it is less visible. 



THE ELASMOPODA {hJALMAR THEEL) A 

 NEW ORDER OF HOLOTHURIDEA 



ALTHOUGH the Holothuridea show a greater tendency 

 to a bilateral arrangement of their internal organs than 

 any other group of the Echinodetmata, most of them are 

 fusiform or cylindrical in shape, and theradiate symmetry 

 prevails so far externally that the five radial ambulacra] 

 vessels and their appendages are similar, that they run 

 symmetrically at equal distances from one another from 

 the oral to the apical pole, and that they are used indif- 

 ferently for the purposes of progression. In all Holo- 

 thuridea, however, two ambulacra, those of the bivhuu, are 

 essentially dorsal, while the three ambulacra of the 

 trivium are ventral ; and in one little group of the 

 ordinary Dendroihirota, which includes the well-known 

 genus Psoitis, a very distinct ambulatory tract is defined 



Viz. i.—Elfidia gladalis, Ihcel. Sid 



on the ventral surface of the body, and the pedicels of the 

 rest of the ambulacral system are either absent or greatly 

 modified. From the form of the ambulatory disk and the 

 position of the mouth and apex, a Cuvieria, with its 

 tentacles expanded, has a very striking resemblance to a 

 large Doris. 



In the year 1875 Dr. Hjalmar The'el, attached as 

 naturalist to Nordenskjbld's expedition to the Yenisei, 

 dredged in the western portion of the Kara Sea at a 

 depth of 150 fathoms, fourteen specimens of a small 

 Holothurian, which he was at first inclined to take for a 

 nudibranchiate mollusc. Elpidia glacialis, Thee), is 

 about 20 mm. long and 8 mm. broad. The anterior por- 



tion is abruptly contracted, so as to give the appearance 

 of a head, and the mouth, surrounded by a ring of ten 

 tentacles, simple with the exception of two terminal papillae, 

 is turned downwards. A transverse section of the body 

 is semicircular, the dorsal surface being strongly arched, 

 while the ventral (trivial) surface is flat, and forms an 

 ambulatory disk. The skin, which has the usual struc- 

 ture of the skin in the Holothuridea, is strengthened by a 

 thick layer of felted calcareous spicules of different forms, 

 with delicate branches which project through the skin, 

 roughening it slightly. Very sparsely scattered, just 

 below the epidermis, there are a few large wheels much 

 like those of Myriotrochus, and a large number of very 

 minute wheels are found in the outer layers of the skin. 

 Elpidia has eight very prominent partially retractile 

 pedicels or water-feet, placed in two opposite rows of four, 

 on the lateral ambulacra of the trivium, along the edges of 

 the ventral disk. Radial vessels are developed in two 

 ambulacra only, the vessels of the ambulacra of the 

 bivium and the central ambulacrum of the trivium being 

 entirely suppressed. The nervous system is radially sym- 

 metrical, five cords running back symmetrically from the 

 oral nerve ring along the five ambulacral lines. Otocysts 

 of peculiar structure are placed at intervals along the 

 course of the nerves. 



On the back there are two rows of paired foot-like 

 appendages much in the position of the bivial ambulacra ; 

 the appendages of the anterior group bend forwards, and 

 those of the posterior backwards. From the absence of 

 the bivial water-vessels these appendages are not in con- 

 nection with the water-vascular system ; they receive 

 twigs, however, from the radial nerves. 



Elpidia is unisexual ; the small genital opening is 

 placed in the dorsal middle-lines about mid-way between, 

 the crown of tentacles and the anterior group of dorsal 

 appendages; the so-called "respiratory tree" and the 

 Cuvierian glands are absent. 



Elpidia is very remarkable both in external form and in 

 internal structure, and differs widely both from the typical 

 Pedata and from the Apoda, in many respects taking an 

 intermediate place between these groups. 



Since the appearance of Dr. Theel's paper Messrs. 

 Koren and Danielssen have described in the Nyt Magazin 

 for Nattirvidenskabernc, two new genera procured by the 

 Norwegian North-Sea Expedition, whose close relation 

 to Elpidia is manifest. The characters of these genera 

 will be given in their place in the systematic list. 



On looking over the Holothuridea of the Challenger 

 Expedition, I at once recognised the resemblance or a 

 large number of the deep-sea species to the form which 

 Dr. The'el had worked out with much care and skill, and 

 acting under the advice of my friend, Prof. Loven, 1 

 asked Dr. The'el to be good enough to undertake the 

 description of the Challenger material belonging to the 

 class, Prof. Lovdn kindly offering his advice and assist- 

 ance. Dr. The'el was over last summer and examined the 

 collection. He recognised over 200 species, half of which 

 are new to science, and of these the greater number from the 

 deep-sea are related to Elpidia. The group enlarged to 

 such an extent, and presenting so many marked pecu- 

 liarities quite revolutionised the faa'es of the Holothuridea, 

 and asserted itself as an order of value equal at all events 

 to that of the Pedata and Apoda. For this order Dr. 

 The'el proposes the name Elasmopoda 



Dr. The'el selected all the forms belonging to the new- 

 order in the Challenger collection, and carried them with 

 him to Sweden, and' a few weeks ago he published, with 

 the permission of the Treasury, in the A". Sv. Vct.-Akad. 

 Hand!., Band 5, No. 19, the first part of a preliminary 

 report on the Holothuridea of the Challenger Expedition, 

 in which seven new genera and seventeen new species of 

 Elasmopoda are defined. 



The following are the genera established by Dr. Theel, 

 and I add the definitions of the two others described by 



