3S Mr. J. D. Macdonald un a Bitentaculate Slug 



VI. — Observations on the Eocternal Characters and Interiial 



Anatomy of a Bitentaculate Slug found at the Island of 

 '^'^'iJAneiteum, New Hebrides. By John Denis Macdonald, R.N., 



Assistant-Surgeon of H.M.S.V. "Torch," Tender to H.M.S. 



'« Herald,'' Capt. Denham, R.N., F.R.S., Commanding the 



Exploring Expedition in the South Seas. 



[With a Plate.] 



At the Island of Aneiteum, in the New Hebrides group, we 

 obtained the only naked terrestrial Gasteropod with which we 

 met during our late cruises amongst the South Sea Islands. 



At first sight the animal appeared to be simply a moderately 

 large species of LimaXj but on closely examining two specimens 

 which Mr. Macgillivray very kindly reserved for me, I noticed 

 that they possessed but the two tentacula that supported the 

 eyes. This character made the further study of their anatomy 

 an object of some interest to me, and I have been induced to 

 draw up the following account of it with the view of determining 

 whether the species may be with propriety retained in, or sepa- 

 rated from, the genus Limax. 



The animal having the power of extending its body consi- 

 derably, or of drawing it up in the longitudinal direction, and 

 spreading it out laterally so as to assume a great variety of 

 shapes, it would b^ rather difficult to state its proportions with 

 any degree of certainty, but it appears to average about 

 2 1 inches in length, by |^ths of an inch in breadth. It is of a pale 

 yellowish-brown colour, varying in depth in different individuals, 

 and often sparingly mottled with a reddish-brown or black pig- 

 ment over the dorsal region. 



Along the middle line of the back a narrow groove extends 

 from the nape to the obtusely pointed extremity of the tail, and 

 from this primary groove, on either side, a number of smaller 

 channels arise, which take a parallel course obliquely outwards 

 and backwards to the thin margin of the foot, and communicate 

 with each other laterally by the transverse interspaces between 

 the soft mammillary elevations of the skin. 



The mantle is of small superficial extent, lying on the right 

 side of the body somewhat in advance of the centre, and circum- 

 scribed by a triangular sunken outline, with the angles gently 

 rounded off. The base of the figure thus formed corresponds 

 with the above-mentioned median groove, which is here slightly 

 deflected to the left, while the outer rather obtuse angle is so 

 deeply notched as to appear to be perforated by the respiratory 

 opening. From the upper and anterior angle two depressed 

 lines pass forwards, diverging so as to include the roots of the 

 tentacula, on the outer side of which they are lost. 



