SOME LITTORAL OLIGOCH ATA OF THE CLYDE. 33 
Tubifex costatus (Clap.). 
This worm was first very briefly described by CLapaREDE in 1863. It was rediscovered 
by BENHAM in material from Sheerness in 1891, and was fully described by him (2), 
especially with regard to its setee and genital organs, in a paper with many excellent 
illustrations. 
The species was placed in a separate genus, Heterochxta, by its original discoverer, 
as well as by Brennan; and this distinction is also assigned to it by Vespovsky (16) and 
Brpparp (1). MicHaAkLsEN, in the body of his work on the Oligocheeta (11), includes 
it in the genus Psammoryctes, but in the appendix (p. 522) unites this genus with . 
Tubifex, and the worm thus becomes J'ubifex costatus. 
SouTHERN (14) records it from between tide-marks on the Ivish coast, but gives no 
description; he refers to its mention by FRimnp, in a paper which I[ have not seen 
(Irish Nat., 1897). Evans (5) records it from the Haddingtonshire coast. 
The worm is thus, apparently, described with any degree of completeness only in 
BENHAM’ paper ; a few additional particulars, and an account of one or two features in 
which my specimens differ from BenHam’s, may therefore be of interest. 
The worms were found at Fintry Bay, about high-water mark, under moist stones, 
at a place where fresh water was running down on to the shore. They live for days 
in half salt, half fresh water. Their average length was greater than that of pre- 
vious records, being about an inch (CLAPAREDE 16 mm., Benwam 3 of an inch) ; 
specimens were met with up to an inch and a quarter. In colour they were of various 
shades of red, the anterior part of the body being paler; as also the genital segments 
on account of the presence of genital products. The number of segments was sixty- 
three to sixty-seven (about forty, BENHAM). j; 
The detailed account of the sete given by Benuam must exhaust the subject. 
Briefly, the sete are all of the ordinary double-pronged type, except those of certain 
dorsal bundles in the anterior part of the body, where they are ‘ palmate’ (segments 
v.—xiv.). I may add that in length the ventral setze in the anterior part of the body are 
about ‘11 mm., in the posterior about ‘086 mm. ; the palmate setz average (095 mm. 
The numbers per bundle in the Millport specimens were rather greater than those found 
by Bennam; thus in the ventral bundles there were up to seven in the anterior part of 
the body, not more than two or three in segments x.—xv., and posterior to this four, three, 
two, or one only ; the palmate dorsal setze were in bundles of six to thirteen, the double- 
pronged. dorsal setze posterior to these in bundles of four, three, two, or one, like the 
corresponding ventral sete. 
BenuAM looked for a long time in vain for intermediate forms between the two types 
of setee. These ‘multidentate’ forms are very common in the Millport specimens ; some 
are figured in fig. 1. As to their distribution, they are found in the segments in front 
of and behind those containing the palmate sete; thus the most anterior dorsal bundles - 
(il. and ii.) may either consist of the usual doubled-pronged setze or of these irregular 
