47 98 Proceedings of 'the Royal Irish Academy. 



Herinides tiideutata sp. n. 

 PL X, figs. 23 a-J. 



Eleven specimens of this new species were found on four different 

 occasions, living in Laniinaria roots in Blacksod Bay. This habitat at once 

 distinguishes it from other allied species of Xerinides, Xerine, and Scolecolepis, 

 all of which live in sand. 



The worms are comparatively small, resembling Spio in appearance. 

 Mature individuals are 16-20 mm. in length, 1-5 mm. in width, and the body 

 is formed of 61-70 segments. The body attains its greatest width in the 

 anterior region, near the 10th segment, and gradually tapers to the very 

 slender tail. The anterior end is blunt, and tapers very little. The dorsal 

 surface is flattened, the ventral surface rounded. In the anterior region the 

 segments are verv short, but in the middle resion thev are almost as long as 

 wide. 



The head (fig. 23 a ) is spindle-shaped, acutely pointed at both ends, the 

 posterior end forming a distinct occipital tentacle. Just behind the middle 

 line of the head are two pairs of black eyes, arranged almost in a straight 

 line. The head is separated from the buccal segment both dorsally and 

 ventrally by deep grooves. The buccal segment forms conspicuous trans- 

 lucent lobes on each side of the head, and is longitudinally folded on the 

 ventral side. The tentacles are short, thick, and firmly adherent, of a deep 

 chocolate colour. The first setigerous segment (figs. 23 A, 23 c ) bears only a 

 ventral bundle of capillary setae, and has no branchia. The setae are in two 

 rows, one consisting of long slender setae, the other of shorter and thicker 

 setae. Behind the setae is a low rounded lamella, and in the dorsal region of 

 the foot are two rounded lobes. The second foot (fig. 23 d) bears two bundles 

 of setae, those in the dorsal region being much the larger. These setae aie 

 all longitudinally striated. The dorsal lamella is large, and completely 

 fused with the branchia, which it slightly exceeds in length. A considerable 

 interval separates the dorsal from the ventral lamella. 



The tenth foot (fig. 23 E) bears two large lamellae which are separated 

 only by a small interval, and are much larger than those of the second foot. 

 The dorsal division has two rows of setae, one row consisting of long slender 

 longitudinally striated setae (fig. 23 H, «), the other row of short thick finely 

 pointed setae, with flattened dotted blades and cylindrical striated proximal 

 shafts (fig. 23 H, b). The ventral setae resemble the short dorsal setae, but are 

 rather shorter and wider. On the lower margin of the ventral bundle is a 

 group of three slender striated setae. 



The branchiae attain their greatest length in the 15th-20th segments. 

 They lie transversely across the dorsum, separated in front by a median 



