PROTULA. 



265 



numerous, united at the base into a short cartilaginous stalk, by 

 which they are attached to the head. Each filament is densely pec- 

 tinated with a ciliary fringe, and, in specimens preserved in spirits, 

 these cilia always assume a unilateral character. Between the tufts, 

 and at their base, is a pair of setaceous tentacula ; and the cephalic 

 segment is encircled with a free cartilaginous wavy margin, which is 

 everted and produced into an obtuse lobe on the dorsal aspect. 

 Thorax of seven equal 



No. XLV. — Protula protensa. 



seven equal seg- 

 ments, margined with a narrow 

 brown skin on each side. In 

 the middle of its dorsal side 

 there is a linear-elliptical area 

 bounded by a dark line, and 

 continued down the abdomen 

 for a short way, when it is lost 

 in the mesial line. The abdo- 

 men consists of numerous very 

 narrow segments, nearly alike, 

 but insensibly narrowed back- 

 wards. Along the ventral sur- 

 face a ribbon-like elevated ten- 

 dinous band runs from one ex- 

 tremity to the other, so that 

 the sides on which the setige- 

 rous feet are placed are di- 

 stinctly defined and depressed. 

 There are seven pairs of feet to 

 the thorax, with an equal num- 

 ber of linear series of uncini : 

 the feet of the abdominal por- 

 tion are very numerous, and the 

 uncini are in a shorter and 

 more elliptical arrangement. 

 The bristles are of different 

 sorts : the fascicle of the tho- 

 racic foot consists of a great 

 number divided into three sets ; 

 — the upper set are of a clear 

 yellowish colour, setaceous, but 

 bent towards the top and 

 brought to a long sharp point 

 with a narrow cutting edge on 

 the outer side of the bend ; — 

 the middle set are stouter and 

 shorter, with a dark lance- 

 shaped point, which is either 

 sti^ight or a little curved ; — 

 and the lower set are weakest, 

 transparent straw-yellow, acicular, the long point being brought to a 

 cutting edge on both sides. There are none of the dark-headed 

 bristles in the abdominal feet,but the re are the two other sorts not 



a. The animal in the shell, natural .size. 

 b. The animal removed from the shell, 

 natural size. c. A single filament of a 

 branchial tuft, magnified. 



