118 Transactions of the Royal Society of South Africa. 



genus Gonospira Swainson, but differs from it in the presence of a tooth 

 on the outer lip, a character which also separates it from Gihhulina expatriata 

 Preston, from Kenya Colony. In fact, there appears to be nothing much 

 like it among African species. 



Gulella tristaoensis Conn., 1922. 

 (Plate IV, fig. 6.) 



1922. Gulella tristaoensis Conn., A.M.N.H. x, p. 115. D. 



Hab. L. Marques. District N. of Macequece (Cressy). 



The type measures 5-3 X 2-3 mm. ; the last whorl, by which throughout 

 all my works I mean the distance from the extreme base of the aperture to 

 the centre of the suture directly above it, a most important measurement, 

 is 2-8 mm. 



The foot of the animal shows distinct peripodial grooves, cutting ofi a 

 rather broad foot-fringe. 



The radula (text-fig. 3) is long and narrow, that of an immature specimen 



5 ^ " 15 16 



I 



Text-fig. 3. — Gulella tristaoensis Conn., Headwaters of River Tristao. 

 Representative teeth from the radula of an immature specimen ; X 500. 



measuring 1-9 X -25 mm. when flattened out. The teeth are of the aculeate 

 type, and are nearly straight except at the anterior or basal end, where 

 they are abruptly curved outwards as shown in the figure. The central 

 tooth is small and degenerate, although furnished with a distinct, sharply 

 pointed cusp. The other teeth increase very slightly in size from the first 

 to about the fourth on each side, and then diminish again towards the outer 

 margins of the radula, the last two or three teeth being as small as the central 

 tooth, and relatively broader and shorter than the larger teeth, which closely 

 resemble one another in form. The apophyses, which are situated about 

 half-way up the cusps, are extremely low and inconspicuous. The largest 

 teeth in each row measure about -03 mm. in length, except near the front 

 end of the radula, where they are scarcely -02 mm. long. In the centre 

 the rows of teeth form an angle of about 120° towards the hinder part of 

 the radula, but the angle becomes more obtuse towards the front end, 

 where the rows are also nearer together, being less than -01 mm. apart. 

 These difierences at the front end of the radula are probably partly due to 

 the immaturity of the specimen. The radular formula is : (17-fl + 17)X 121. 



