82 PERCY SLADEN TRUST EXPEDITION 
slightly nearer the dorsal than the ventral side, arises the process which is 10mm. high 
and ends in the three branches which sometimes themselves give rise to short secondary 
branches. In one specimen the operculum is overgrown with a branching Bryozoon, but 
in the other two cases it is quite smooth. 
The branchial crown is five-spiral and 15 mm. high. 
The thorax to the front of the collar measures 9 mm. long and about 7 mm. wide, and 
is composed of the usual seven segments. The abdomen, with nearly 200 segments, is 
36mm. long and 6 mm. across its widest part. The ventral surface is very distinctly 
segmented and has a deep feecal groove. 
The collar is entire ventrally, but folded inwards in the centre so as to appear at first 
sight to have a median fissure (fig. 7a). Two specimens thus appear to have somewhat 
rounded ventral lobes, while the other has two triangular lobes very much like those of 
Spirobranchus giganteus shown in fig. 6 a. 
The collar setze are as usual in the genus (fig. 7 5). 
There were about 12 of these and 12 plain ones with a fringe on one side instead 
of a distinct blade. 
The thoracic uncini are enormous (about 300, long) and have 26 teeth, the most 
anterior one being long and hollowed out underneath like a gouge (figs. 7¢ andd). The 
abdominal ones are much smaller, with only 14 teeth (fig. 7 e), in front of the anterior 
gouged one is a small process. The abdominal setae are as usual (fig. 7 f) in the genus. 
13. Spirobranchus semperi, Mérch (87) 1863; Willey (50) 1905. 
Serpula quadricornis Grube (24) 1878. 
Specific characteristics: 1. Operculum flat, with four distinct spiny horns. 2. Uneini 
with 9—13 teeth. 38. Branchial crown forms only one turn of a spiral. 
Localities. Zanzibar and Red Sea. 
14. Spirobranchus senvperi, Morch, var. acroceros, Willey (50). 
Specific characteristics : this only differs from the above in having a conical opercular 
dise with the four horns, reduced in size, at the top. 
Localities. Numerous specimens from Suakin Harbour and Agig Bay; also three 
from Dongonab in the Red Sea and several from Zanzibar in Mr Crossland’s collections ; 
one specimen without its operculum from Suvadiva, Maldive Group, in Prof. Stanley 
Gardiner’s collection. 
From the four first places both varieties are represented. The tubes are generally 
rough with longitudinal ridges and much overgrown with Bryozoa, &c. One which 
contained the var. a@croceros and is not much overgrown is triangular, with a distinct 
notched median keel ending in a projection over the aperture. Collar very ample, entire 
and much folded ventrally and with small processes internal to the dorso-lateral lobes. 
The opercular plate resembles Grube’s figure (24 Taf. xv. fig. 6) very closely. The 
two dorsal horns divide into two main tines quite close to their bases, whereas the two 
ventral generally only give rise to short processes. These horns are often hidden by 
Hydrozoa, debris, &c., and in one they are united and altogether hidden by a colony of 
