POLYCH^ETA OF THE FAMILIES SERPULID^E AND SA DELUDE. 91 



Genus Spirorbis Lamarck, 1801. 



Characteristics of genus and sub-genera have been given in full (15, pp. 

 792-799). 



Sub-genus Paralseospira Caullery and Mesnil (1, p. 202), emend. Pixell (15, pp. 795 

 and 799). 



ix (intarc^icus n. sp. 



Specific characteristics : 



1. Collar-setae a few small finely striated simple blades, fig. 3, c. 



2. Third thoracic fascicle contains some bladed sickle-shaped seise. 



3. Abdominal setae, flattened trumpets with one side produced. 



4. Tube triangular in section and generally very regularly coiled (fig. 3, ). 

 Locality. Several specimens growing on fucus, dredged at Station 325, April 1903, 



Scotia Bay, South Orkneys; lat. 60 43' 42" S., long. 44 38' 33" W., in 9 to 10 

 fathoms. 



The large thick tubes are almost perfectly triangular in section and very regularly 

 coiled to form a disc, with concave upper surface, and measuring up to 4 mm. across 

 (fig. 3, ). There are nearly always young tubes attached to them, one specimen bearing 

 as many as twelve of different sizes. In this they resemble CAULLERY and MESNIL'S 

 (l, p. 203) Spirorbis aggregates. 



The opercular plate may be flat, convex, or conical, but has in every case a thin 

 flattened talon. Small circular perforations occur in the calcareous plate, and through 

 these project small membranous projections, which are generally thorn-shaped. Though 

 the opercula vary so much, there is no doubt that all the variations should be included in 

 the same species, for there are intermediate forms between the thin, flattened plate, 

 which seems to be characteristic of young specimens, and the conical form. It is also 

 very questionable whether details as to the shape of the operculum are ever sufficiently 

 constant to be of much value in specific determination. 



Many of the specimens are of very large size, some measuring over a centimetre in 

 length. There are nine long branchiae : the second on the left is transformed into the 

 pedicle of the operculum, and is slightly larger than the others. 



This species could only be included in the sub-genus Paralneospira, provided that 

 the modified characteristics as suggested in a previous paper (15) be adopted for it, 

 owing to the fact that it differs from all previously described Paralaeospira in 

 having simple blades for the collar-setae (fig. 3, c). These are remarkably small, and 

 there are only seven on each side, so that the whole fascicle is very insignificant. 

 The other thoracic fascicles are much larger, and the uncini are about 40 mm. 

 long. There are about twenty abdominal segments following a rather long aseti- 



gerous region. 



(ROY. soc. EDIN. TRANS., VOL. XLLX., :!:>!.) 



