3 o ORDERS OF FORAMINIFERA. PAET in. 



segments are connected by sarcode filaments passing 

 through, the minute apertures in the partitions between 

 the chambers, so that the whole constitutes one com- 

 pound creature. 



Although the character and structure assumed by the 

 semi-fluid bodies of the known Foraminifera have been 

 determined in most cases with admirable precision, it 

 is still thought advisable to arrange them according to 

 the substance of the shell : consequently they form three 

 natural orders; namely, the Porcellanous or imperfo- 

 rate, which have calcareous shells often so polished and 

 shining that they resemble porcelain; secondly, the 

 Arenaceous Foraminifera, consisting of animals which 

 secrete a kind of cement from their surfaces, and cover 

 themselves with calcareous or siliceous sand-grains ; and 

 lastly, the Yitreous and Perforated order, which is the 

 most numerous and highly organized of the whole class, 

 has siliceous shells transparent as glass, but acquires 

 more or less of an opaque aspect in consequence of 

 minute straight tubes which perforate the substance of 

 the shell perpendicularly to its surface, and consequently 

 interfere with the transmission of light. 



Order of Porcellanous Foraminifera. 



The Miliolidse constitute the porcellanous order, which 

 consists of twelve genera and many species, varying 

 from a mere scale to such as have chambered shells of 

 complicated structure. 



The genus Miliola has minute white shells resem- 

 bling millet seeds, often so brilliantly polished that they 

 are perfectly characteristic of the porcelain family to 

 which they belong. No Foraminifera are better suited 

 to give an idea of the intimate connection between the 

 shell and its inhabitant than the Miliola, the funda- 

 mental type of this genus. The shell is a spiral (i, fig. 97), 



