162 



THE VOYAGE OF H.M.S. CHALLENGER. 



dredged on the northern coasts of Europe. The relative abundance of genera and species 

 in these dredgings, compared with those at similar depths around Bermuda, was remarked, 

 and will be referred to again when comparing the dredgings along continental shores with 

 those at similar depths around oceanic islands. A Boltenia-like Ascidian, belonging to 

 the new genus Culeolus, was taken for the first time in the dredging in 1700 fathoms, 

 and is referred to in the following notes by Professor W. A. Herdman of University 

 College, Liverpool, on the Tunicata collected by the Expedition : — 



The Tunicata. — " The large collection of Tunicata made during the Expedition has 

 added greatly to our knowledge of this interesting group, especially as regards its 

 distribution. The pelagic Tunicates (the Salpidse, the Doliolidas, and the Pyrosomidse), 

 which form such an important constituent of the surface fauna of the ocean, have, on 

 account of their abundance and the comparative ease with which they may be obtained, 

 been much studied in many parts of the world. Hence the Challenger collection of these 

 forms contains few novelties, but is of great value, since, from the constancy and care with 

 which tow-net observations were conducted, and their results preserved, it affords much 

 additional information as to the distribution of these pelagic Tunicates horizontally, and 

 to a less degree vertically. 1 



" The remarkable new genus Octacnemus described by Mr. Moseley 2 (see fig. 64), of 

 which two species are known, seems to be an abyssal and considerably modified ally of 

 the pelagic Salpidse. 



" The collection is rich in Compound Ascidians, but although many of them are new 



species, the great majority belong to common 

 and well-known genera. This can be ac- 

 counted for by the fact clearly brought out 

 by the Challenger Expedition, that the Ascidias 

 Compositse form essentially a shallow water 

 group, the bulk of the collection having been 

 obtained close to land, or at localities, such as 

 Kerguelen Island and Port Jackson, where the 

 shore fauna was investigated. A few Com- 

 pound Ascidians were, however, obtained from 

 great depths, such as 1600, 2050, and 2900 fathoms* but they show no notable 

 morphological peculiarities. 



" The horizontal distribution of the group is very wide, representatives being found in 

 all the great oceans and in almost all latitudes. 



1 For details, see the forthcoming Report on the Tunicata, Part II. 



2 Moseley, Tram. Linn. Soe. Lond. (Zool.), ser. 2, vol. i. p. 287, 1877 ; see also Report on the Tunicata, Part I., 

 Zool. ChalL Exp., part xvii., 1882. 



Fio. 64. — OctacnemvAbythiu8,'Ho$eiey. Schematic, vertical, 

 anil longitudinal section, through the animal, along the 

 middle line, ia, Mouth ; m, opening of the cesophagus ; 

 r, rectum and anus ; ea, cloacal aperture ; rm, rm, 

 radiating muscles ; n, nucleus ; mh, muscles of the 

 nucleus ; g, respiratory membrane ; b, thickened margin of 

 the base ; pa, pedicle of the attachment. (After Moseley.) 



