210 HOGH WATSON. 



unknown, and it is to be hoped that further specimens will 

 be discovei-ed so that these organs may be described. 



Apera burnupi Smith. 



Apera burnupi Stnith. Ann. Mag. Nat. Hist. (6tli ser.), 1892. vol. x, 

 p. 466. 



Apera natalensis CoUinge, Ann. S. Afr. Mus., 1900, vol. ii, p. 3, pi. i, 

 figs. 3, 4, pi. ii, figs. 14, 15; Simroth, Naturwiss. Wochenschr., 1901, 

 vol. xvii, p. Ill, fig. 7; Simroth, Bronn's Klass. u. Ordn. d. Tier- 

 Reichs III, Gastr. Pulm., 1909, p. 143, fig. 42 c, pi. iv, figs. 9. 10 ; 

 Collinge, Ann. Natal Mus., 1910, vol. ii, p. 167 ; Simroth, Bronn's 

 Klass. u. Ordn. d. Tier-Reichs III, Gastr. Pulm., 1912, p. 611; 

 Connolly, Ann. S. Afr. Mus., 1912, vol. xi, p. 63. 



External Characters (PI. VII, figs. 10, 11; PL A^II, 

 fig. 26; and 'Ann. S. Afr. Mus,/ vol. ii, pi. i, figs. 3, 4). — 

 Animal broad and flattened towards the hind end, tapering 

 anteriorly, with four longitudinal keels, two on each side 

 of the body. Notwithstanding the two pairs of keels 

 the animal is squarish in section, excepting posteriorly, 

 as the lower keels ai-e not far from the edges of the foot. 

 Upper keels prominent though blunt, nearly parallel to each 

 other in the middle of the body and separated by about 

 seven- eighths of the breadth of the animal. Anteriorly they 

 converge a little towards the head. In the posterior three- 

 eighths of the slug the upper keels become very prominent, at 

 first diverging and then curving round to meet in a very 

 obtuse angle above the posterior extremity of the foot (but 

 the angle is probably less obtuse in young than in adult 

 specimens). They thus enclose a large flattened oval area, 

 sloping downwards and backwards, and having the respira- 

 tory opening slightly in front and to the right of its centre. 

 Lower keels less prominent, twice as far from the upper keels 

 as from the edges of the foot, extending for nearly three 

 quarters of the length of the animal but not reaching the 

 hind end. Foot rather broad, but tapering behind as in the 

 other species, so that the posterior dorsal expansion of 

 the body overhangs the edges of the foot on each side. 

 Outer lip of respiratory opening rather nai'row, exposing the 



