278 SOMK MOLLCSCS UF XATAL LACiOOXS. 



ill llic spire tliat I liave seen, lias the spire less eroded than I 

 have seen in any large specimen, has the plaits on the columella 

 lip, or ' shelf,' better developed, and the gray colour is unusual." 



From Tongaat and Umkomaas I have collected an almost 

 hlack Tlieodoxus which is quite distinct from naialcnsis. Mr. 

 Burnup says: " The coihng of the whorls is quite different. It is 

 very like T. gagates Lam, from Mauritius, etc. (a species not 

 hitherto recorded Irom South Africa), coiled in the same way and 

 with the red stain on the ])arietal callus; the opercula, too, seem 

 to correspond exactly, but I have no specimen of gigates so finely 

 itiarked with zig-zag yellow lines." 



In October, 1920, I collected specimens of. Septaria, a genus 

 new to the South African list, from the Umbogintwini lagoon. 

 This operculated shell of brackish water belongs to the family 

 Neritida?. I have now found numerous examples in the Umko- 

 maas lagoon and others at Karridene, Illovo and Amanzimtoti. 

 Those from the Umkomaas lagoon appear to include two distinct 

 forms, one broad with very short septum ; the other narrow, with 

 longer septum. A difference in colour markings seems to coincide 

 with the diffei'ence in shape. The larger shells weie proportionally 

 narrower than the younger sliells. 



At Umbogintwini I foimd O.rij.sfclc fabuhni.s Ki-auss, which 

 would also appear to be an occasional inhabitant of brackish water 

 in lagoons. 



IXHABITAXTS OF FllESH WaTER IN LAGOOXS. 



In an overflow pool which drains into the Urngeni lagoon and 

 contains quite fresh water, I have found numerous examples of 

 Tiara fuherculata. and Modiola capensis. Three of the Modiolae 

 were finer than those in the Burnup collection, but a little short 

 of Kraiiss's type, which is almost 22 mm. long. My longest w^as 

 19 mm. Some of these Modiola? were infested with cercariae 

 whose tails were divided for the complete length. The Tiarse 

 were heavily infested with cercariae, resembling ('. cawstoni. 

 This cercaria is closely allied to that responsible for Lung Fluke 

 disease in the Far Fast, which is contracted through eating the 

 crabs in which the cercariae have encysted ; so that the presence 

 of numei'ous small crabs in the pools at the Umgeni mouth where 

 Ti'^tra fuherculata exists in great numbers may be of some 

 im]K)itance. 



High up the Illovo lagoon, in an overflow pool, I found several 

 examples of SnJueriiit)). Mr. Burnup reports: " I think it must 

 be Sphcrriiim. fcrrugineutii Krs, which does not seem to have been 

 collefted in South Africa since the types were taken in 1846. 

 ('onnolly collected it at Victoria Falls." On the same water- 

 weeds I found some land shells, Succinea, probably ])afcnfis- 

 fiinin — a rare form which Mr. Burnup has once found at the edge 

 of tlie Umgeni lagoon. 



I am told that when the river subsides numerous bivalves, 

 about half-an-inch in length, are to be found on the rocks at the 

 mouth of the Umbogintwini. 



