47 74 Proceedings of the Royal Irish Academy. 



Mystides (Mesomystides) elongata sp. n. 

 PI. V, fig. 12. 



A number of badly preserved specimens were dredged in Clew Bay in 

 24 fms., accompanied by tbe remarkable fauna already noted. Tbe same 

 species was afterwards obtained in better condition in 20 fms. in Dingle Bay. 

 Tbe specimens are sometimes yellowisb green when preserved, sometimes very 

 dark green. The body is very slender and elongated, the segments being 1- 2 

 times as long as broad, the posterior ones being more elongate than those in the 

 anterior region. The anal region is missing in all the specimens. The largest 

 fragment is 6 mm. long, composed of 80 segments, but the entire animal is 

 probably considerably longer. In the 5th segment the width of the body is 

 •11 mm., or including the setigerous lobes - 25 mm. The width gradually 

 increases to the middle of the body. The head (fig. 12a) is twice as long as 

 broad, with rounded anterior margin. In the posterior lateral angles are two 

 eyes composed of transversely elongated patches of brown pigment, without 

 lenses. Eising from the anterior border of the head are 4 long, slender 

 tentacles, the dorsal pair being slightly longer than the ventral pair. The first 

 segment bears a single pair of long slender tapering cirri. The second segment 

 bears two pairs of cirri, a dorsal pair slightly longer than those on the first 

 segment, and a short ventral pah - , similar to the ventral cirri of the succeeding 

 segments. Xo trace of setae or spines could be found on the second segment. 

 The third segment bears on each side a normal setigerous lobe with setae and 

 a ventral cirrus, but the dorsal cirrus is missing in all specimens. The 

 setigerous lobe and ventral cirrus in each segment gradually increase in size 

 up to the fifth segment, where they attain the normal size and shape. 



The normal foot (fig. 12b) has a long bluntly pointed setigerous lobe 

 provided with a single spine and four setae. The dorsal cirri are small and 

 fusiform. The ventral cirri are longer than the dorsal cirri, slightly swollen 

 in the proximal half, and attached near the middle of the setigerous lobe. 

 Towards the posterior end the ventral cirrus increases in length, and its point 

 of attachment moves towards the tip of the setigerous lobe (fig. 1 2c). 



The setae of this species are very characteristic. There are four in each 

 foot, of two different types. Three of them have compound tips (fig. 12b, b, c). 

 The shaft is thick, curved, and bevelled, but not swollen at the tip, which is 

 bifid. The terminal piece is short, wide at the base, tapering to a fine point, 

 and with very coarse striations, which give it an appearance markedly different 

 from any other British species. The second seta from above differs from the 

 other three (fig. 12b, a). The shaft is decidedly thinner, and terminates in a 

 flattened coarsely striated expansion, which is prolonged on one side to a fine 



