Correspondence — R. H. llastall. 93 



With regard to the genera Sinocystis and Ovocystis which 

 Dr. Bather would unite, it is regrettable that when he had the actual 

 figured specimens to examine his customary accuracy of observation 

 seems to have been wanting, so that he has been led to doubt the 

 presence of certain characters which I described. Indeed, he 

 candidly admits (Geol. Mag. for November, p. 513) that he did not 

 notice one of the structures in question till he had read my memoir 

 and sent back the specimens. It must be accordingly concluded 

 that his remarks are partly based on the casts and figures with their 

 unavoidable defects and limitations. Two points may be specially 

 mentioned. (1) Sinocystis loczyi. Of the many specimens of this 

 species which were submitted to me for study, of which only a few 

 were figured, it was observed that only in a very few instances was 

 the summit of the tubercles missing and the diplopores exposed, and 

 that this was due to abrasion, as clearly shown by the condition of 

 the rest of the theca. In both large and small specimens the 

 uninjured surface of both species of this genus possessed a thick 

 layer of epistereom covering the tubercles and concealing the 

 openings of the diplopores. In Ovocystis mansuyi, on the other 

 hand, the diplopores were always seen to open freely on the surface, 

 whether the specimens were large or small, worn or undamaged. 

 The good preservation of much of the material which passed through 

 my hands seems to render these facts beyond doubt. (2) The 

 runnels on the surface of Ovocystis mansuyi, to which I applied the 

 term "food-grooves" with perhaps too easy an assumption of their 

 function, are more or less distinctly seen in a large number of the 

 specimens which I examined, and are frequently quite conspicuous 

 features impossible to confuse with the normal depressions between 

 the plates of Sinocystis or Ovocystis itself, though Dr. Bather believes 

 that they are of this nature and devoid of significance. It is true that 

 they have not come out well in the collotype reproductions and much 

 less in the casts on which he relies, but there can be no question as 

 to the existence of these strange and often irregular grooves on the 

 surface, whatever view we hold as to their character. If Dr. Bather 

 had had the advantage of studying the large series of specimens 

 which I had, and of observing the different degrees of development 

 of these runnels, he would not have questioned their existence. 

 Whether the differences between Sinocystis and Ovocystis are 

 sufficient to separate them generically after taking into account these 

 and other points which I mentioned may be a matter of opinion, but 

 the presence and constancv of such characters have to be admitted. 



F. 11. C. Beed. 

 Cambridge. 



December 18, 1918. 



THE GENESIS OP TUNGSTEN ORES. 

 Sir, — In reply to Mr. J. Coggin Brown's letter in the January 

 number of the Geological Magazine on the Genesis of Tungsten 

 Ores I should like to state that my paper on that subject was 

 written in the first two months of 1918. The valuable lecture by 

 Dr. Jones was reprinted in the Mining Journal in March, 1918, but 



