BRITISH SILURIAN BRACHIOPODA. 89 



the acid must be resolutely set aside, and reliance must be placed solely upon scraping 

 with a knife, with many and repeated ablutions in water, until every trace of film of spar 

 is removed from the surface of the spirals. Success in this operation of course requires 

 practice so as to reveal perfectly the whole of the spirals without scraping away any 

 portion of them. The knife to be used should be a large, single-bladed one, with a 

 rounded and not hook-shaped point, and a part of the blade should be tied round with 

 thick string so that it may be held firmly in the hand, as the end only of the blade should 

 be used. Of course the knife will frequently need to be sharpened. The specimen to 

 be operated upon should be held in the left hand and not rested upon any object. This 

 prevents jarring, and enables the operator to nicely regulate the force which he applies 

 with the knife. 



" When the spirals are clearly revealed, free from every film or trace of the sparry 

 matrix, the worked surface should be rubbed still more smooth by fine emery cloth, and 

 then dipped for a few seconds only in the dilute acid in order to remove the dullness 

 produced in working, when the dark lines of the spirals will be seen in clear and beautiful 

 relief in the light matrix. 



" In a large number of cases the spirals will be found in the sparry matrix in a 

 fragmentary condition, or broken from the hinge-plate and displaced — specimens in such a 

 condition are rarely worth the trouble of working. Now, it is a comparatively easy task 

 to develop the spirals in the manner above described, but it is much more difficult to 

 reveal their connections with each other, or their connections with the hinge-plate. Kach 

 genus requires some modification of method to achieve this end ; indeed, for the develop- 

 ment of each kind of spiral connection there is one way pre-eminently the best, and this 

 way can only be discovered after many attempts and not a few failures, but once having 

 discovered the right way the task becomes comparatively easy. 



" The best way in each case is that which reveals, clearly and openly, in one and the 

 same specimen, and in unbroken sequence, the connections of the spirals with the hinge- 

 plate and their connections with each other, and this of course necessitates the scraping 

 away in various directions of certain parts of the spirals. Mr. Davidson has figured 

 specimens in several cases {e.g. of Whitjieldia tmnida and Merisia Herculea, &c.) in the 

 exact condition in which I worked them, and the study of these figures will be of more 

 use than any mere verbal description. I may observe in passing that, as a rule, those 

 specimens only are suitable for the developing of the connections of the spirals, the interiors 

 of which are entirely sparry, or which are sparry under the beak. In the figured examples 

 referred to I first of all carefully removed the whole of the sparry matrix from the exterior of 

 the spirals, being very careful in so doing not to injure the connection with the hinge-plate. 

 Then I worked away the spirals from the ventral side until the specimens were in the 

 condition in which they are figured. In very small specimens showing the spirals, and in 

 most of the specimens showing the connections of the spirals, I have omitted the use of 

 emery cloth, because of the danger of destroying some of the fine lines which need to be 



