THE HYDROIDS OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 57 



reduced from " about two-thirds " to about one-half. As seen from the anterior aspect 

 the hydrotheca appears to be covered in by only two opercular flaps, the free margins 

 of which run from the tip of one lateral tooth to that of the other ; but when a 

 lateral view of the colony is obtained, so that one can look directly on the operculum, 

 another line is seen running from the mid point of the horizontal line connecting the 

 lateral teeth to the median superior point of the aperture. This line presumably marks 

 the margin of two contiguous flaps of the operculum, and it would therefore seem that 

 three, and not two, are present. The determination, however, is one of considerable 

 difficulty owing to the delicacy of the operculum. The downward projecting processes 

 from the base of the hydrotheca are long and evident. 



Measurements : 



Internodes, length ..... 0'63-0'78 mm. 



breadth ..... O'05-O 06 



Hydrotheca, length of contiguous portion . . 0'22-0'25 ,, 



free portion * . . . 0'21-0'22 ,, 



,, diameter near base . . . 0'08-0'09 



at aperture . . . O'OS-OOQ 



Locality. Growing upon seaweed (Codium, sp.) from Station 81, Abrohlos Bank, 

 Brazil. Lat. 18 24' S., long. 37 58' W. 36 fathoms. Bottom deposit, coral. 20th 

 December 1902. 



Serlularia heterodontaj n. sp. 



Growing upon the surface of a seaweed (Codium, sp.) in company with S. rathbuni 

 and S. cornicina are numerous colonies of this more minute form. The simple 

 unbranched stems arise from a creeping stolon and cover the weed as with a coat of 

 delicate hairs. At first glance the colonies are hard to distinguish from those of 

 S. rathbuni, but on close examination their minuteness and delicacy render them 

 distinct even to the unaided eye. The largest are only 6 mm. in height, 3 '5 to 4 mm. 

 being much more common. The hydrorhizal tube has a diameter a little greater than 

 that of the stem, and is strengthened in places by chitinous processes projecting down- 

 wards from its roof or upwards from its floor. 



The stems are divided into fairly regular internodes separated by distinct nodes. 

 At the base two oblique nodes occur in succession, cutting off between them a short 

 lozenge-shaped athecate internode. The remainder of the internodes are long and 

 slender, narrower at the proximal end and very gradually increasing in diameter 

 upwards, until by a sudden dilation at the top they form a broad bracket upon which 

 the hydrothecse rest. The thecate internodes are separated by straight nodes, but 

 occasionally an oblique node occurs in addition, a small athecate internode being in 

 such a case intercalated between the longer thecate individuals. 



* The " free portion " is measured from the line of the stem to the tip of the lateral teeth. 



t (Tf pos, other ; and <Woj, a tooth, indicating the presence of other than the usual marginal teeth. 



(BOY. soc. EDIN. TRANS., VOL. XLVII., 79.) 



