QUBKETT MICEOSCOPICAL CLUB, 195 



in numbers. (2) All three deposits repeat genera, but not as a 

 rule species. This tends to confirm the idea that the deposits are 

 not of the oldest origin, evolution having had time to alter 

 species, to adapt them to local environments, but no time to 

 influence the genera. (3) On the other hand, some species and 

 even genera are peculiar to one or two of the deposits and show 

 no variation. Thus Simbirsk and Mors both contain Odonto- 

 tropis carinata and 0. hyalina, neither of which have been found 

 anywhere else except in Franz Joseph Land. Simbirsk has several 

 peculiar genera, such as Lepidodiscus, Pyrgodiscus, and Chelonio- 

 discus. Janischia antiqua is peculiar to Mors. Oamaru is the 

 richest in species, but has no particular genus. (4) Some genera, 

 such as Triceratium, Hemiaulus, and Coscinodiscus, have left more 

 intermediate forms, and are consequently very difficult to classify. 

 (5) The genera Chaetoceros and Rhizosolenia are absent from all 

 three. This may be because these diatoms thrive in shallow 

 coastal waters and the deposits are strictly pelagic. Sir Nicolas 

 then stated a few conclusions : (1) Mors is the poorest in species 

 and Oamaru the richest — suggesting that warm waters are con- 

 ducive to variation. (2) Individual and varietal variation 

 approach the continuous method, while specific and generic varia- 

 tions tend towards quasi-discontinuity. (3) The evolutionary 

 ladder appears to be continuous, but " mutations," or non-con- 

 tinuous variations, as exemplified by cases of " sports " among 

 plants and animals, exist. 



The Barbados deposits show affinities with those of Oamaru, 

 especially in the presence in both of genera such as Brightwellia, 

 Craspedodiscus and Porodiscus, in which the centres of the discs 

 have structures difiering from that of the rest of their surfaces. 



Dr. A. Smith Woodward spoke of the value of diatoms in the 

 correlation of rocks, and after some remarks by Messrs. A. E. 

 Hilton and N. E. Brown, a hearty vote of thanks was accorded to 

 Sir Nicolas YermolofE, on the motion of the President, for his 

 valuable paper. 



The President then called upon Mr. C. D. Soar to give an 

 abstract of his paper on " Water Mites of the Genus Eylais." Mr. 

 Soar said that the genus was established by Miiller in 1776, and for 

 100 years it remained represented solely by Eylais extendens. 

 The genus is notable in that the hind pair of legs is not used for 

 swimming. Eventually it was discovered that what was con- 



