32 



ON A CASE OF PRESUMED VIVIPARITY IN LIMICOLARIA. 



By G. C. RoBsoN, B.A. 



(By permission of the Trustees of the British Museum.) 



Bead 8th December, 1911. 



In September of the present year Mr. H. E. Preston received some 

 living specimens of Limicolaria from South- West Uganda and Belgian 

 Congo. Two species were represented — L. Smithi and a new species 

 as yet undescribed. After some time the uterus, in both cases, 

 was found to be full of apparently well-developed young. In 

 view of the fact that viviparity is not a phenomenon of frequent 

 occurrence among Mollusca the matter was deemed worthy of some 

 consideration, and Mr. Preston kindly handed the specimens over to 

 me to report upon. 



In the new species the young are well advanced, are all totally 

 free from any envelope, and already show traces of coloration 

 upon the shell. In L. Smithi, however, the majority are still encased 

 in a thin membrane of a soft and pliant nature which is attached 

 to the mouth-region by a chaliiza-like structure, remains of which are 

 to be seen in the young of the previously mentioned species. The 

 young of L. Smithi are fairly well developed, and the shell has 

 advanced considerably beyond the rudimentary stage. The envelope 

 has disappeared over nearly all the region opposed to the aperture of 

 the shell. The parent in this case contained also three or four eggs 

 with hard shells. These had been perforated in situ in two or more 

 places, and contained only some loose tissue of doubtful nature. 



The specimen of the unnamed species certainly, then, is viviparous. 

 Can we say the same of the specimens of L. Smithi? The young 

 were certainly encased in a membrane; but as a matter of fact the 

 latter in nearly all cases was frayed away and perforated over all 

 the aperture of the shell. On considering the difference in degree of 

 development between the two species I am inclined to think that the 

 condition seen in L. Smithi is an early stage of the complete freedom 

 from enveloping structures seen in the new species. 



The question that arises out of these data is whether this is 

 actually a case of normal viviparity, and further whether the genus 

 Limicolaria as a whole is viviparous. 



We may briefly deal with the latter consideration by saying that, 

 as far as can be made out, no references to the reproduction of this 

 genus are to be found in the literature of Pulmonate ontogeny. 

 Achatina, a very near relative, has several ovoviviparous species 

 (1,2,3). 



Turning to our first question, we should be careful before we accept 

 this evidence as proving that Limicolaria is viviparous. It is possible 

 that the young in these two species may have been retained longer in 

 the uterus of the ])arent than is natural under ordinary circumstances, 

 owing to the change in environment to which they had been subjected. 



