SPIRORBIS PUSILLOIDES. 397 
presents a minutely cellular or reticulated structure when viewed by a high power from above, 
and a series of concentric rings. A considerable process or talon occurs beneath it, the 
lower edge of which varies in outline—sometimes being irregular, at other times smooth. 
The distal concavity frequently contains mud and minute alge. 
The body has the typical coil, three bristled segments occurring in front, and twenty to 
thirty posteriorly. The most powerful muscle seems to be that on the concave side of the 
coil. The collar-bristles (Plate CX XXIII, fig. 3) have straight shafts dilating into a broad 
web at the base of the tip, which is bent backward, is of moderate length, finely tapered 
and minutely serrated. The basal web is striated, each of the striz ending in a sharp point, 
whilst on the distal blade the strize slant obliquely to the serrated edge. The second tuft 
has bristles with rather broad wings, and the blade tapers somewhat suddenly to a very 
fine point, so as to give a character to the bristle. The third tuft has both winged 
(Plate CX XXIII, fig. 3a) and sickle-shaped bristles, the edge of the latter being serrated. 
The posterior bristles (Plate CX XXIII, fig. 3b) are minute, and project little beyond 
the surface. They are geniculate, the tip being bent nearly at a right angle to the shaft 
and coarsely serrated. 
The anterior hooks are stated by Miss Pixell to be of ordinary shape, with about twenty 
teeth. In outline (Plate CXXXIII, fig. 3c) they are somewhat triangular, the anterior 
edge having a closely set series of fine teeth, the last, representing the main fang, being 
larger with a narrow gulf behind it. 
The tube is described by Miss Pixell as dextral, large and flat, thick and opaque, slightly 
roughened, but without definite growth-lines. A slight median ridge is present, and some- 
times one on either side; the aperture has, however, an entire margin and measures 2 mm. 
across. The Irish examples from Blacksod Bay were in dense clusters on stones and shells, 
sometimes only the aperture being visible, whilst the tube itself formed a lax spiral quite 
different from the original account of Miss Pixell, though it is still large. In lateral view 
the elongated spires of some of the masses gave an unusual depth to the Spirorbid coating. 
Some examples, indeed, formed an elongated spiral tube after the manner of the horn of the 
Indian antelope or even that of the koodoo. Originally the tube appears to be small and 
flat, then as the annelid increases in size the tube thickens, becomes loosely spiral and keeps 
pace with the growth of sponges or other encrusting growths, so that its rounded and dilated 
aperture (trumpet-like in some) is free. From Miss Pixell’s description the tubes follow 
another mode of growth under different circumstances. 
Reproduction.—Mature specimens were found in September, and incubation takes place 
in the tube, where strings of the ova occur. 
B. Incubation in Operculum. 
4. SPIRORBIS PUSILLOIDES, De St. Joseph, 1894; an var. 8S. PAGENSTECHERI, De Quatrefages. 
Specific Characters —Cephalic lobe bounded by a collar of the normal type and ciliated. 
Branchie three on each side, the filaments terminating in a process about the length of a 
barbule. The second on the right bears the operculum, which is cylindro-conical and has 
a brood-pouch guarded posteriorly by a calcareous (?) plate. Body 1:20 mm. in length ; 
