Yol. 55.] DR. A. W. ROWE ON- THE GENUS MICEASTER. 547 



results. For 40 years it has been uncertain whether the varieties 

 of Chalk Micraster have been formed by spasmodic individual 

 variation, or form part of a continuous variation in time — that is, 

 Are they circuli or mutations ? The question could not be settled in 

 a museum, or from a priori zoological considerations, as the differ- 

 ences in question, if found in recent Echinids, would not be 

 regarded as of specific value. The final decision rests on the 

 historical method, of zonal collection on a large scale, which has 

 been adopted by the Author. The mass of facts in the paper 

 would be of the highest value. Some of the differences in question 

 are probably due to the depth at which the Micrasters lived. 

 He congratulated the Author on founding his Micraster proecursor 

 on a group of specimens, instead of on a single type. 



Mr. E. T. Newton remarked on the thorough and philosophic 

 character of the Author's methods of work. Having had the 

 opportunity of seeing the work as it progressed, and of testing its 

 applicability to the determination of the horizons of the Chalk, from 

 the Bhynchonella Cuvieri-zone to that of Micraster cor-anguinum, 

 he was satisfied that it rested on a sure foundation, and would in 

 future be a great help to geologists working in these Upper Cre- 

 taceous rocks. 



Mr. G. E. DiBLET said that he spoke as a held- worker, though a 

 comparative novice, and could most thoroughly appreciate the lucid 

 diagnostic features which the Author had so admirably put before 

 them. He felt sure that the many perplexing points regarding 

 the genus, especially in those species ranging from AI. cor-hovis 

 upward to M. cor-anguinum, would now disappear. He placed great 

 faith in the Author's work, as, in sending specimens to him from 

 various areas and zones, he had in every case determined their exact 

 zonal derivation. He most heartily congratulated the Author on his 

 valuable paper, and at the same time tendered his thanks to him for 

 his kindness in determining many of his (the speaker's) specimens. 



The President, Mr. C. D. Shbrborn, and Prof. Sollas also spoke. 



The Author, in answer to Prof. Seeley, said that he could trace 

 a perfect transition, not only in the general shape of the test, but 

 that the transition applied to every feature of the test, even in the 

 minutest detail. The Author added that specific types were rare, 

 and that transitional forms preponderated. He further stated that 

 though the facies of the Micrasters might vary slightly in different 

 localities, still the observations on the essential features of the test 

 were perfectly reliable, even in sections so far apart as Dover and 

 Beer Head. Iq reply to Mr. E. T. Newton, the Author pointed out 

 that he had been forced by lack of time to leave out the discussion 

 of the group of M. joroecursor, but that the arguments in favour of 

 such a group were fully set forth in the paper. He also replied to 

 various remarks made by other speakers, and, in conclusion, thanked 

 the Fellows for the reception accorded to his paper. 



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