THE PLANKTON OF THE FAROE CHANNEL AND SHETLANDS. 359 



to place specifically owing to its mutilated condition, but it does not 

 appear to agree with any of the five species described by Haeckel 

 (p. 1589, Chall. Jiej)-), none of which are North Atlantic forms. It 

 is therefore interesting to note the occurrence of the species in the 

 North Atlantic. The characteristics of the radial tubes are quite 

 peculiar. 



CHALLENGEPJDA (J. Murray, 1876). 



These singular organisms are not uncommon* round the Shetland 

 waters and in the cold area of the Faroe Channel, and I have taken 

 them both in surface and deep tow-nettings. One species, captured 

 by me off the north coast of Shetland in a surface tow-netting, 

 appears to be new. 



Challengeron walwini, n. sp. Plate II., Figs. 1, la. 



The shell, which is longer than broad, presents the usual " dia- 

 tomaceous " structure. Its margin has twenty-five spines, of which 

 that at the aboral pole is the largest ; on each side of tliis spine is 

 a very short spine. The other spines round the lower edge are 

 long, though not so long as the apical spine, and progressively and 

 regularly diminish in size towards the peristome. The latter 

 presents two lateral slightly curved and divergent teeth and a 

 dorsal bifid tooth. All are beset with short and sharp spines. There 

 is no pharynx. 



Dimensions. — Length of the shell, '18 mm.; of the body, 11 mm.; 

 of the peristome, "07 mm.; of the lateral teeth of the peristome, 

 •03 mm.; of the principal aboral spine, -03 mm.; breadth of the 

 shell, -09 mm. 



This animal would appear to belong to Haeckel's subgenus 

 " Challengerosium " ("margin of the shell dentated or serrated with 

 a continuous series of numerous short radial spines"), all of which, 

 with the exception of one (as to which the depth is not stated), 

 C.joMnnis (taken in the Faroe Channel, Gulf Stream), are deep-water 

 species, and tropical or Pacific. 



It was captured at Station V., February 9th, 1900, at the surface. 



It is closely related to C. willemcesii (Haeckel), but differs in having 

 a smaller number of marginal spines (in C. willemoesii these are fifty 

 to sixty), and the spinulation of the peristome also differentiates it 

 from this. 



* In some hauls, e.g. Station Al, in August, 1900, tlicy were captured in great quantity 

 in the Mesoplankton, chiefly at 350 fathoms. 



NEW SERIES. — VOL. VI. NO. 3. 



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