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. siinrothi v. Graff [3]. 



ft Nervous system normal. 



PI. pellucida (Martens) [3]. 

 '^ PI. pelagica (Moseley) [1]. 



/3. Non-pelagic. 

 PI. graffii Lang [1]. Mediterranean. 



PI. folium (Ersted [1]. Mediterranean, North Sea. 



PI. 'reticulata 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 ,, 



c? aperture from " mouth " 2*5 ,, 



2 „ „ 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 difierent 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 



