POLYMNIA. 125 



bristle-tufts in front assume the form of papillae. Marenzeller mentions that the 

 setigerous processes are crenate at the convex tip, but this was not evident in those 

 examined. 



The first hooks occur opposite the third setigerous process — that is, the second behind 

 the branchiae — and they occupy the summit of the elevated ridge which extends from the 

 bristle-tuft downward to the ventral grove, and cover, in short, the external aspect of the 

 ventral longitudinal muscles. They are in a single row in the first six segments, but 

 the rest are in a double row, and this continues to the commencement of the last thirty. 

 After the cessation of the bristles the uncinigerous processes form transverse crescents in 

 each segment, gradually, however, becoming smaller, until on the slender terminal region 

 in front of the tail they form a series of papillae, so that the ventral ridge on each side is 

 moniliform. The first hooks are distinguished (Plate CXXVa, fig. 2 b) by the great size 

 of the main fang, which has a crown of small hooks above it, about three being usually 

 visible in lateral view, and by the comparatively small size and oblique nature of the base, 

 which has above its dorsal angle an abrupt incurvation, whilst on its anterior edge it has 

 a sharp point, for the attachment of a tendon, and a gentle incurvation beneath it. The 

 modified form of these early hooks is indicated by the imperfect condition of those at the 

 end of the row. By-and-by they form a double row aud assume the typical condition in 

 which the great fang is proportionally smaller (Plate CXXVa, fig. 2 c), the base less 

 elongated, its lower edge more convex, and the curve below the point on the anterior 

 edge less pronounced. About four small hooks are visible above the great fang in 

 lateral view. 



The Amphitrite Tondi of Delle Chiaje 1 (1828) is a form having two branchiae, but the 

 description is so brief, and the figure so indefinite, that it is uncertain whether it refers to 

 A. scylla or not. 



This species was entered by De Quatrefages (1865) under two titles, 'viz., Savigny's, 

 and again as the Phys alia gracilis of Grrube. 



A form with three branchiae, but otherwise closely resembling the above in the 

 cephalic region, intersetigerous papillae, bristles and hooks, occurs occasionally between 

 tide-marks in Guernsey and Herm. It would appear to be] another instance of the 

 variability of these organs (branchiae) in a common species. 



De St. Joseph (1894) describes a single pair of segmental organs in the third 

 segment, with a ciliated funnel internally, and a reddish-brown outer region which opens 

 between the setigerous process and the row of hooks. 



Two preparations from Polperro in the British Museum, labelled " Terebella 

 constrictor" contain Amphitrite scylla, Nos. 62.7.12.50, and 62.7.12.46. 



Genus CXLV. — Polymnia, Malmgren, 1865. 



Cephalic lobe with a large collar, and at its junction with the body a series of 

 eye-specks, whilst a frilled inward curve occurs at each lower edge. Second, third 

 and fourth segments with small lamellae. Anterior ventral shields larger than the 



1 ' Memorie/ vol. iii, p. 169, tav. xlv, fig. 2. 



