244 SABELLA B.C. 



make a series of circular bands, as in 8. penicillus and other forms, thus conferring great 

 beauty on the expanded organs. In some cases when mounted the reddish-brown 

 pigment is in isolated masses at intervals along the filament and patches occur on the 

 terminal process. There are about 11 filaments on each side springing from the central 

 region of the cephalic plate, a basal fissure, most distinct ventrally, occurring dorsally 

 and ventrally. They are connected only at the base and free throughout the rest of 

 their extent, and are long tapering organs with proportionally short pinnse, which as 

 they reach the tip gradually diminish in length, and end in a series of short papillge 

 at the base of the terminal strap-shaped tapering process. The chordoid skeleton is 

 continued along the centre of the flattened tip, and into each pinna. In young forms 

 the pinna3 are short, but the flattened terminal strap is well developed. 



The body is comparatively small, elongated, and distinctly segmented throughout—a 

 f eature*characteristic of the species. Segments fifty-six, but the tail in the majority of the 

 examples was in process of reproduction, so that the actual number of segments must exceed 

 the figure mentioned. The body is widest in front and gradually tapers behind the middle 

 to the posterior end, where the rounded anus is terminal. The dorsal surface is more or 

 less rounded, the ventral flattened and marked by the scutes from end to end. A slight 

 depression occurs in the mid-dorsal line anteriorly, and continuing to the right behind the 

 sixth bristle tuft it crosses the seventh segment obliquely to the middle line at its posterior 

 border, whence it passes to the tip of the tail, cutting the ventral scutes into two in each 

 segment. Six bristled segments are present in the anterior region and five uncinigerous 

 rows, but occasionally only five and four occur respectively. Other variations, apparently 

 arising from lost parts in process of reproduction, show the ventral furrow running to 

 the front, or a diminished number of anterior ventral scutes. Moreover, the two anterior 

 scutes may be split by a furrow quite independently of the main ventral furrow. The 

 first setigerous process is situated behind the collar, and is inconspicuous. It has a 

 small tuft of simple bristles with acutely tapered tips and narrow wings as in the dorsal 

 group of the anterior region. The bristles of the succeeding segments of the anterior 

 region (five in number) have dorsally translucent bristles with straight shafts and finely 

 tapered tips and narrow wings, the upper having longer and more delicate tips, and 

 ventrally narrow, spatulate forms (Plate CXXVIII, fig. 1 a), the outline of the wings 

 being more or less a long ellipse, the tapering shaft being continued as a fine process 

 distally. Moreover, those with broader tips form a shorter row than those with more 

 elongated tips. The outline of the tip of the latter bristles thus essentially differs from 

 that in Potamilla reniformis and also from those of P. Torelli. In the posterior region 

 the bristles form a tulip-like fascicle with a knee or curvature on each bristle toward 

 the end of the shaft, the convexity with the wings being external. Those with the 

 longest and most delicate tips (Plate CXXVIII, fig. 1) are dorsal, those with slightly 

 broader wings (fig. 1') are ventral, and the former are most conspicuous near the tip of the 

 tail. In the anterior region five uncinigerous rows lie to the ventral edge of the setigerous 

 processes, their inner ends impinging on the scutes opposite them. The first commences 

 opposite the second bristle-tuft, and all are longer than those of the posterior region. The 

 hooks (Plate CXXVIII, fig. 1 b) are in a single row with a main fang and a series of serra- 

 tions above it, a neck of moderate length, with strise where it enlarges into the boldly 



