OCR Text |
Show 102 MR. F. F. LAIDLAW ON POLYCLADS [May 26, B. Species in which the penis is armed with spines only. a. Pelagic forms. t Nervous system much decentralised. PI. simrothi v. Graff [3]. ft Nervous system normal. PI. pellucida (Martens) [3]. ? PI. pelagica (Moseley) [lj. j3. Non-pelagic. PI. graffii Lang [1]. Mediterranean. PI. folium CErsted [1]. Mediterranean, North Sea. PI. reticidata Diesing [1], Sandwich Is. nee Stimpson. Planocera nebidosa Verrill [2] is probably not a member of the genus Planocera s. str. PARAPLANOCERA AURORA, sp. nov. (Plate IX. fig. 1.) Body almost circular, margin crenellate. Shore form. Length 15 mm. Breadth 12-5 „ " Mouth " from anterior- end 7'5 „ Tentacles ,, ,, 5*0 „ d aperture from " mouth " 2"5 ,, ? „ „ male "5 „ Length of receptaculum seminis 3*0 ,, Tentacles apart 1 '0 ,, The coloration of this beautiful species is shown in PI. IX. fig. 1. In general it is of a rich rose-pink, becoming more intense towards the margin, and mottled with lines and spots of yellowish white. The tentacles are pink, and the mid-dorsal region white. The gut-branches are six in number-. The arrangement of eye-spots and appearance of the genital apparatus are shown in the accompanying figure (text-figure 3, p. 103). The genital organs have an arrangement in general precisely similar to that found in the other species of the genus [6]. The antrum masculinum is small, lined with ciliated epithelium. The penis is a coiled muscular tube {p.), its walls consisting of circular and radial muscle-fibres. Its lumen is lined with chitinous spines of two different kinds, those near the distal end of the penis being large and irregular, whilst further- forward {i. e. away from the antrum) the spines become small and thorn-shaped. These two kinds of spines merge rather- gradually into each other. Some way in front of the antrum a thin outer layer- of circular-fibres detaches itself from the wall of the penis, to form an outer sheath which remains attached to the ventral side of the penis for some distance, so that it is only at its proximal, anterior, end that the penis is completely free from the sheath. The space |