12 Transactions of the Society. 



to a frequently repeated bursting off of its cemented stones, and 

 simultaneous insertion of new structural materials, such as larger 

 stones and mortar mass." Nor can we accept his statement that 

 as the shell increases in diameter towards the adult condition, the 

 flat surfaces of the sand-grains are turned outwards so as to produce 

 the smooth exterior surface of the adult shell. Our reasons for 

 differing from him will appear later on in this paper. 



The whole basis of Dr. Ehumbler's identification ( Vereinigung) 

 of the two species seems to start from Brady's misleading expres- 

 sion " interstitial orifices " being applied by him to the growing or 

 " Psariimosphaera stage " of Saccammina. He, however, states with 

 no uncertain voice the principal argument against his own theory. 

 He says (6, p. 465), " the maximum size of Psammosplidera (4 mm.) 

 seems at first sight to be incomprehensible. At such a size the 

 Saccammina, form ought plainly to have asserted itself." 



This is a patent and unanswerable fact, and it is not disproved 

 or shaken by Dr. Ehumbler's suggestion that the turning round and 

 tucking in of the projecting corners of the grains to produce the 

 smooth shell-wall of adult Saccammina, reduces the diameter. If 

 anything, it would be the other way about, by reason of the larger 

 surface now exposed on the periphery of the shell. Dr. Ehumbler's 

 further argument based on the differences of magnification in 

 Brady's figures is not borne out by the facts, and his argument that 

 the lighter the colour of the cement the younger the test, although 

 in the main correct as regards some species, is not a tenable theory 

 as a whole. In many dredgings the same species may often be 

 found presenting two well-marked groups in all stages of growth, 

 one with nearly white cement, the other deeply ferruginous. Am- 

 mocliscus incertus, Vemeuilina polystropha, and Bigcnerina digitata 

 may be mentioned as typical examples of this tendency to vari- 

 ation, which entirely upset the theory that colour depends upon 

 age. Moreover, some species of Hgperammina and Beophax are 

 noticeable by the deeper colour of the cement around the orifice of 

 the latest chamber. When, again, Dr. Ehumbler proceeds to analyse 

 this phenomenon with measurements of the constituent particles 

 which he finds (p. 4H7) to be from 3855 millionths to 547 hundred- 

 thousandths of a millimetre, we confess we are unable to keep pace 

 with him. 



In a later and still more important work {IJ/), Dr. Ehumbler 

 reverts to this matter of shell growth. He says (p. 157), " a 

 troublesome enlargement takes place, certain parts of the shell- 

 wall are broken open and are arranged with a larger volume by 

 the insertion of new building stones. Thus, deformations of tlie 

 test come about, which are only readjusted by later renewed 

 insertions of material." This process he felicitously describes as 

 intercalar growth, wliich, he asserts, is assisted by a partial loosen- 

 ing of the cement by chemical action of the sarcode-body. But if, 

 as Dr. Ehumbler suggests, the shell is thus gradually reconstructed 



