306 NATURAL SCIENCE. November. 



enough to clear with a tooth-brush the top of the test and the first 

 row of spines ; but, after that, no real headway could be made, as the 

 knife could only dig the chalk off the test, and no brush could work 

 between the lower rows of spines. The dental-engine, with its 

 revolving brush no more than -2% inch in diameter, soon solved the 

 difficulty, and cleaned the specimen so thoroughly that the little 

 spatulate spines were left in situ, and not a fragment was broken off. 



It may not be out of place to give the measurement of the 

 brushes which have proved to be most generally useful. The brushes 

 are made of hard and soft bristle, and of badger-hair, and they can 

 be made of any length and thickness so as to suit the taste of the 

 worker. 



Small bristle brushes i. length ^ in. diameter /^ in. 



ii. 

 iii. 



Small badger-hair brushes ... ,, 



Large and hard bristle brushes , 



Large badger-hair brushes ... , 

 With brushes like these one can do most things. Cidavis sceptrifera 

 was cited as an example of what the engine can do, but this is coarse 

 work compared to much that can be achieved by this instrument. 

 The delicate Plocoscyphia convoluta of the soft Margate Chalk can be 

 cleaned out so that chamber opens into chamber, and a bristle may 

 be passed from one cavity to another, the hexactinellid mesh being 

 left intact, and the walls of the convolutions standing out unbroken, 

 though no thicker than a stout visiting card. This sponge, to the 

 best of my knowledge, has never been worked out before, and, but for 

 the round-pointed knife and the dental-engine, it would probably 

 still be undeveloped. 



But even more striking than this is the result obtained with the 

 Bryozoa, especially with the delicate branching Cyclostomata. Here, 

 instead of being content with tediously hand-brushing a fallen frag- 

 ment, one can take a colony, with its intertwining branches, and 

 clear all the matrix away, leaving the beautiful structure supported 

 by only a few points on the block, with every cell sharp and clear. 

 In my collection there is a colony of Pustulipora pustulosa, two inches 

 square, with branches under -^f^ of an inch in diameter, cleared in 

 this way, and so delicate is the work of the engine that not a particle 

 of the branches was broken off in the process. Reticnlipova obliqua can 

 be taken out of the matrix, and all the mesh-work cleared out, so 

 that not an atom of chalk remains. Such delicate Bryozoa as 

 Entalopiiora proboscidea, Vincularia regularis, Heteropora francquafia, and 

 the like can be displayed on the matrix with a badger-hair brush, 

 without the least damage to the specimen. 



The student of Foraminifera, Entomostraca, and Bryozoa, who 

 has the good fortune to work in a district where spongiform flints 

 abound, has his task made easy, for the flint-meal will yield him 



