212 HUGH WATSON. 



of A. natalensis according to Colliiige, and of the still 

 larger specimen belonging to the South African Museum 

 shown in PL VII, fig. 10 : 



Length . . . . .65 mm. . 77 mm. 



Breadth between upper keels 



in middle . . . . 10 „ . 12'5 „ 



Breadth between upper keels 



behind respiratory opening . 13*5 ,, . 17 ,, 



Breadth betw^een lower keels 



in middle .... — . 14'5 „ 



Breadth of foot-sole . . 9".5 „ . 11 "5 „ 



Greatest height (15 mm. in front 



of respiratory opening) . — .14 ,, 



Distance from respirator}' open- 

 ing to hind end ... — .1 8"5 „ 



Internal Characters. — Skin extremely thick, especially 

 towards the hind end (PL IX, fig. 30). Shell (PL XIII, 

 fig. 49) 5'5 X 3*2 mm., of moderate thickness, convex, w-ith a 

 conical apex projecting slightly beyond the posterior margin ; 

 sinus rather deep. 



Pedal gland (PL XIII, fig. 56). — Exceptionally large, 

 its loops wrapping round the other organs; glandular 

 tissue extending throughout its entire length. 



Nervous system. — Buccal ganglia situated anteriorly; 

 connectives short. 



Digestive System (PL XYII, figs. 108, 109; PL XX, 

 fig. 128; text-fig. 4, D, p. 161; PL XXI, fig. 133).— Radula 

 (of large specimen) 6mm. long; central tooth present, with a 

 vei-y short single cusp ; eleven laterals with short double cusps, 

 and more than twice as many marginals with long, narrow, 

 nearly straight cusps, on each side, the transition between 

 latei-als and marginals being abrupt ; formula (of large speci- 

 men) : (25 -l-11 + l-fll-f 25) X 77. Odontophore small, with 

 a single slender buccal retractor; odontophoral support bluntly 

 pointed in front. CEsophagus narrow and as long as the 

 salivary ducts ; crop cylindrical ; intestine narrow^, first loop 

 deep, posterior continuation on right side of liver. Salivary 



