ON SOME PLYMOUTH HOLOTHUEIANS. 229 



Colochirus is examined it may be found to be similar to that in C. saxicola 

 and C brunnea. 



With regard to the Group B given above, it is an interesting fact that 

 Norman himself (2, p. 382) states that some of his specimens (which 

 have been shown to belong to C. saxicola) would be placed by some 

 naturalists in the sub-genus Colochirus merely on account of the characters 

 of the dorsal ambulacra, and also that Herouard placed what is almost 

 certainly C. saxicola in that very genus as Colochirus lacazei. It is not 

 improbable, therefore, that when the European Cucumarians are revised 

 the whole of the genus Cucumaria may be divisible into two groups 

 similar to those given above, and that those specimens having the 

 characters of Group B may have to be designated as species of the genus 

 Colochirus. 



PART II. 



ON THE OCCURRENCE OF CUCUMARIA ELONGATA DUB. 

 AND KOR. AND THYONE RAPHANUS DUB. AND KOR. 

 IN THE PLYMOUTH DISTRICT. 



During the period from March, 1911, to Sept., 1912, numerous specimens 

 of Cucumaria elongata Diib. and Kor. were obtained at various stations 

 in the Plymouth district. These specimens were nearly all taken in a 

 dredge with a fine-meshed net, worked from the Laboratory steamer 

 Oithona. The depths from which these Cucumarians were dredged 

 varied from about 5 to about 30 fathoms, and the nature of the bottom 

 in which they were living was almost invariably muddy, but varying 

 from fine mud in Plymouth Sound and off Rame Head, to muddy gravel 

 in the region about 2 miles south of Wembury Bay, and to fine muddy 

 sand on the Rame-Eddystone Trawling Ground. (See 16 and 17.*) 

 There can be little doubt that C. elongata is fairly common in this district 

 on all the muddy grounds, and is probably not uncommon on the fine 

 sand of the outer grounds. 



The captures of this species have been made at 15 stations within a 

 small area, so that the distribution can be described with reference to 

 the various grounds already defined in earlier volumes of this Journal 

 (16* and 17) as follows : — 



Plymouth Sound. On one occasion (18th May, 1911) 4 specimens 



* See these references for a description of the grounds in the Plymouth district. Since 

 those accounts were written in 1899 and 1904 there has been a good deal of mud deposited 

 on the various grounds just outside the Sound from dredgings in the harbour. 



