62 INVERTEBRATE PALAEONTOLOGY 



non-calcareous matrix, strong caustic potash may be 

 used, but it is not invariably effective, and needs 

 complete removal before the specimen is dried. 



Mechanical means for removal of matrix are more 

 generally applied than chemical ones, and give more 

 scope for individual skill. It is a good plan to leave a 

 small portion of rock on the specimen, if this is possible 

 without hiding some essential structure. The matrix 

 not only affords a clue to the horizon from which the 

 fossil came (invaluable in event of loss or displacement 

 of the label) but may serve to suggest the conditions 

 under which the organism lived. In attacking the 

 matrix near the fossil, pressure is better than blows. 

 The direction of pressure should always be perpendicular 

 to the shell- surface. Never scrape or scratch the 

 material ; try to ease it off in chips or grains. If the 

 rock gives way suddenly, and the tool touches the 

 specimen, only a prick will result if these precautions 

 are taken ; otherwise a slash or groove will disfigure it. 

 Similarly a pointed tool is better than a knife. The 

 most efficient implement is a thick needle (set in a 

 handle), ground to an angular, blunt pyramid at the 

 tip. In many cases it is helpful to keep the specimen 

 under water, and to watch the removal of each grain 

 under a binocular dissecting microscope. 



(Ill) DISSECTION OF FOSSILS 



With the exception of Echinoderm tests, Invertebrate 

 hard-parts are normally external structures. They often 

 exhibit superficial excrescences and other ornament that 

 have but slight relation to actual anatomy, useful though 

 they may be for specific identification. The anomalous 

 position is often reached where the species to which a 

 fossil belongs can be readily determined, while its generic 



