50 .Mr. Brockbank on 



into which these limestones may be classed polished by a 

 marble mason — and there were then to be seen some in- 

 dications of shells and coprolites, but still none of the 

 Entomostraca. Next I had a set of thin sections of each 

 of the limestone groups ground down and prepared for 

 the microscope — a difficult operation with a limestone of 

 a very fossiliferous and brecciated structure. The ex- 

 periment was successful, and the result exceeded my 

 expectations. 



The following are my notes of a few examples of the 

 eight or ten sections of limestones now produced : — 



No. 3 group limestones shows the marble to be made up of 

 small organisms, amongst which are beautiful sections of oval 

 shells cut through at varying angles, some shewing the 

 hinges and the overlapping of the bivalve shells. The 

 thinness of the substance of the shells points to Ento- 

 mostraca^ and of these there are several forms present. One 

 form appears to be Cypridina Primoeva (see Prof Rupert 

 Jones' monograph — " Entomostraca of the Coal measures "). 

 Of this variety some have oval carapace valves, and some 

 pyriform, and both these occur here. There are also many 

 filiform objects, which may be either antennae, or very small 

 bones — some show a tubular structure under a high power,, 

 others have a cellular structure. 



In another example from No. 3 group I note on the 

 marble polished surface : — This is spotted all over with 

 Spirorbis in great profusion, and with pale yellow circular 

 markings, varying from half an inch diameter to tiny round 

 spots, all indicating the presence of fossil organisms — some 

 thousands to the cubic inch. The microscope reveals many 

 interesting shells of Entomostraca, but having more sub- 

 stance and more oblate curves than in the former examples ; 

 the overlap of the valves is beautifully shewn (probably 

 Cytherelld). Many other small organisms are crowded into 

 the field of view. 



