1889.] 



On some Variations of Cardium edule. 



207 



(a.) The change in proportion does not occur in all shells, nor to an 

 equal degree in those in which it is found. 



(&.) This variation is far more marked in shells of greater absolute 

 size, making it necessary that samples of shells of nearly the same 

 size must be taken for comparison. 



(c.) This variation occurred slightly in the sliells of the 2nd 

 terrace, increasiugly in those of the 3rd and 4th, reaching a point in 

 the 5th terrace which is practically not afterwards exceeded, even in 

 shells found as much as 30 feet lower, though the changes in texture, 

 &c, had greatly progressed in these latter. (See tables.) 



In this lake shells of Dreissena polymorpha were found on the level 

 of the 3rd terrace, and shells of Hydrobia ulvce on most of the terraces, 

 which did not differ f rom those of the Aral Sea. 



Jaksi Klich is the largest superficially of the three dry lakes con- 

 taining cockles. Its length is about 10 miles and its breadth 3 

 miles. It differs from Shumish Kul in being comparatively shallow, 

 the former having been about 60 feet deep before the separation from 

 the Aral Sea, while the latter cannot have been more than 15 — 20 

 feet deep. There is no distinct series of terraces on its banks, but 

 the shells occur in two chief deposits, an upper and a lower deposit. 

 The outer deposit marks the original high level of the water, and the 

 other forms a band of shells round the salt which now fills the bottom 

 of the lake. 



Generally speaking, the shells of the lower deposit show the same 

 variations in texture, colour, shape, &c, when compared with those 

 of the upper deposit, as were found in the case of the shells of 

 Shumish Kul. But while the shells of the highest terrace at Shumish 

 Kul were practically the same as those now living in the Aral Sea, 

 those of the upper deposit at Jaksi Klich differ in some particulars, 

 probably in connexion with the fact that Jaksi Klich was always only 

 a shallow lagoon, while Shumish Kul was a deep lake. 



The variation in the proportion of length to breadth reaches a 

 greater development in the shells of the inner deposit at Jaksi 

 Klich than in any other shells examined (see tables), excepting those 

 of the fresh water lake, Ramleh, No. 2. 



Jaman Klich is a small, independent lake-bed, about half a mile in 

 diameter and about 15 — 20 feet deep. Its shells show the same 

 variations as those of Jaksi Klich. ( See tables.) 



On the flats between Shumish Kul and the other two lakes are a 

 considerable number of very large shells of Cardium edule. These 

 shells , have special characters, and perhaps form a distinct variety. 

 Some of them were found at the bottom of Jaksi Klich and Jaman 

 Klich, also in a small dry lagoon, lately separated from the Aral Sea, 

 near Alta Kuduk. As will be hereafter mentioned, similar shells 

 were found deposited in great numbers beneath the surface-soil at 



VOL. XLVI. q 



