412 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



unique brown color. Examination in polarized light suggests that 

 the wall of one large group of porcellaneous Foraminifera, the milio- 

 lids, must be made of minute, randomly oriented crystals. A bright 

 line observed at the surface of the tests suggests that a thin layer of 

 crystals with parallel orientation exists at the surface. 



Carbon replicas of the surfaces of miliolids reveal two sorts of pat- 

 tern present. In one case (pi. 1, fig. 1), there appear to be numerous 

 stubby crystals of calcite randomly oriented. The crystals do not have 

 well-developed faces, but even appear to be cylindrical in some cases. 

 The ends are flat or rounded. The crystals are all about the same size, 

 about 2 ju, long and i/o /^ wide. The general appearance is chaotic, 

 like a jumble of short sticks, and indeed there seem to be numerous 

 spaces between the tiny crystals, so that the wall may be porous even 

 though it is not perforated by pores. Other surfaces (pi. 1, fig. 2) show 

 a striking pattern of tiny thin rhombohedral crystals, all having more 

 or less the same orientation. These crystals, like the others, are about 

 2 fx long and i/^ ju, wide. They are, however, distinguished by the 

 presence of sharp crystal faces, and they are very thin. The pattern 

 resembles the slate or shingle roof on a house. Often groups of two 

 or tliree crystals appear to be joined by fine sawtooth sutures between 

 the crystals. On some specimens the shingle pattern can be observed 

 to overlie the layer with marked randomly oriented crystals. 



The main part of the wall of a miliolid is seen to consist of a mass of 

 more or less randomly oriented tiny crystals, and might actually be 

 somewhat porous. The surface of a fresh miliolid test is covered by 

 a veneer of the shingle crystal layer, and it is this layer that reflects 

 light, producing the glistening appearance of the test. This layer 

 is easily removed by corrosion revealing the randomly oriented matted 

 layer, which is nonreflective, producing a dull surface. 



Thus details of the structure of the miliolid wall, which could only 

 be suggested by observations in the light microscope, have been re- 

 vealed by electronmicroscopic examination of the tests. The size, 

 shape, and distribution of the units of which the wall is constructed 

 are now known. Some questions, such as the cause of the brown color 

 observed in transmitted light, remain temporarily unanswered, and 

 a host of new questions arise from examination of the elect ronmicro- 

 graphs. How is the matted layer of crystals in the wall produced? 

 Is the shinglelike surface layer deposited before or after the rest of 

 the wall? How are the crystals held together? What is the mean- 

 ing of the sawtooth sutures between some crystals in the shingle 

 layer? As is common in science, the development of new techniques 

 results in solving some problems and suggesting many new, more pene- 

 trating questions to be asked of the objects of study. 



The hyaline, or perforate, Foraminifera are extremely important to 

 micropaleontologists for it is among this group that are to be found 



