40 I'ltOCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



and some obscure niarkings beneath it are visible through, the thin, 

 transparent dorsal region. A yellow spot (PI. V, Fig. 1, i/.s.) on the 

 left side near the posterior end of the mantle looks as if it were the 

 nacleus of the shell ; this, however, is an illusion. The rest of 

 the integument is smooth, with scarcely a wrinkle ; indeed, it is 

 difficult to trace the boundary of the foot-fringe (which I have named 

 the " Sohlenleiste " ) by means of the parapodial groove (pedal-groove 

 of Pilsbry). Only two tentacles are present, viz. the ommatopliores. 

 The genital opening is situated immediately behind the right tentacle, 

 and appears as a fissure slanting obliquely towards the foot. In front 

 of the foot- sole there is a broad transverse groove, as in all Stylom- 

 matophora. The mouth is situated directly above and almost within 

 this groove, and is bounded on either side by a labial lobe. These 

 lobes do not meet, a small free space being left immediately above the 

 mouth itself. It thus offers a contrast to Hijalimax Maillardi, the 

 upper lip of which presents a more complete arc. No osphradium 

 (" Geruchsleiste ") was observed beneath the mantle margin. The 

 upper surface is of a very pale ochre colour, with a shade of lilac, 

 principally on the surface of the mantle ; greyish or blackish spots are 

 scattered over it. The tail has two black bands shading otf laterally. 

 Hows of fine spots mark the median neck groove and the margin of 

 the foot. The whole skin, though preserved in a firm condition, is 

 transparent ; hence it may be inferred, from analogy, that during life 

 all the organs can be distinguished through the integument. 



T/ie mantle-sac and the sliell. — The mantle encloses a large cavity, 

 which is completely filled by the shell. This latter is a small fiat 

 plate of 9 mm. in length, and 6mm. in breadth (PL "V, Fig. 3). It 

 did not appear to be attached at any point to the base of the cavity. 

 Eeneath the light-yellowish periostracum the lime was deposited in 

 concentric rings, with an excentric nucleus to the left of the posterior 

 end. The nearer the nucleus, the thicker is the shelly matter. The 

 periphery is solid, surrounded, near the posterior right-hand margin, 

 by a brown conchiolin line. The nucleus is somewhat thickened ; the 

 shell throughout is perfectly flat, and therefore does not enclose any 

 of the soft parts. In Hijalimax it is slightly arched (Fischer). One 

 is surprised to find that the yellow spot in the mantle is not over 

 the nucleus of the shell. This spot forms the undermost layer of 

 the mantle itself (PI. Y, Fig. 5). It is structureless and of a hard 

 cartilaginous nature. The black spot above it is situated on the 

 surface. It consists, not of a single chromatophore, but of a group. 

 I consider, however, that the yellow spot is the primitive shell. 

 This is demonstrated by its structure and position ; for if the shell 

 in the course of its growth increased slightly at its posterior end, 

 the primitive shell, between which and the integument there is a 

 singularly close connection, could not fail to become separated from it. 



The pallial organs. — The membrane which constitutes the floor of 

 the mantle cavity also forms the roof of the pulmonary chamber 

 (PI. V, Fig. 4), of the pericardium, of the nephridium, of parts of the 

 liver, and of the intestine. The floor of the pulmonary chamber 

 is smooth, colourless, and transpai-ent. The details shown in Fig. 4 



