African iVoti-tudiinc Mollimca. ■\>^0 



18 in number, iiicri'iisiiifj^ in size from 1 to 0, wliirh is the 

 ljir}^ist, and diminisliiiif^ tlicnce to 10; 10 to l(\ snbef|ual, 

 17 rather smaller than 1(5, 1^5 ihc smallest. Xnmljer oC lows, 

 imrhulin^ nascent, 5 1. 



Murconia elyonennis (Preston), 1913. 



It lias not been possible to examine the raduhc, but, 

 jud^iny; from the siiclls alone, this species aj)pears to be 

 widely distributed to the north and east oF L. Victoria 

 Nyanza, linvinj^ been colleeted on Mt. Elgon ( Wood lio use), 

 the Uasin Gislui Platean (Mrs. Barber), Malange, Mabira 

 Forest {Diininicr), and the Darugu River Valley (/farries). 

 The animal resembles in colonr that of J/, maryarita. 



While varying little in form, this species shows enormons 

 variation in size, especially at a distance from the type- 

 locality, in tlie Darugu R. valley, where examples range 

 from lOo- np to 15 mm. in length, while in the Cedar Forest 

 on the Uasin Gishn Platean, on the eastern slope of Mt. 

 Elgon, the average length is rather sniallcr than that of the 

 type, being only 9 mm. 



The gradual and regular range in size is shown in a series 

 from various districts in tigs. 43 to 48 and 52 to 57 on 

 PI. XIV., among whieli may also be observed a marked 

 difference in comparative width between examples from the 

 same locality, the lower sutures being noticeably more 

 oblique in the more slender shells. 



Genus Ptychotre.ma, Miircli, 1852. 



Ptychotrema jjsheri, sp. n. (IM. XIV. fig. 32.) 



Shell comparatively large, cylindrical, rimate, rather solid 

 and silky, semitransparcnt, pale lacteous-olivaeeous. Spire 

 produced, sides nearly parallel, ape.K hemispherical. Whorls 

 8, nearly flat, first 4 rapidly increasing, remainder nearly 

 equal, sculpture consisting of oblicpie transverse strije, ex- 

 tremely close and faint on the first 4 whorls, more distant 

 and much stronger, especially below the suture, on the 

 remainder ; suture shallow, subcrenulate. Aperture (piad- 

 rate, narrowing at base ; peristome continuous, white, 

 shining, broadly reflexed ; dentition consisting of a strong 

 fold at the angle of paries and sinus, concave on its right 

 and entering as far as can be seen within the shell ; opposite 

 this is a single supra-palatal denticle, below which is a large 

 inrunniug fold, corresponding to a deep external furrow 



