14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 'J'] 



to impossible to determine the species of most foraminifera from 

 thin sections alone. In the case of certain of the Orbitoid genera such 

 as Lepidocyclma, etc., sections are of great importance as many of 

 the specific characters are based on the internal structure. 



Unless something is known of the external appearance from other 

 sources it is usually very difficult to even make generic determinations 

 from rock sections. Certainly many of the genera of the Rotalidae 

 cannot be told from one another in section, and the same is true of 

 other groups. It is sometimes possible with hard material to break 

 out whole specimens. This can be done by grinding or by breaking 

 the rock in various ways. 



CLASSIFICATION 



There have been many classifications since the earliest one of 

 d'Orbigny made in 1826. In most of the works' of late years ten 

 famiHes have been recognized, one of these, the Gromidae, being 

 confined largely to fresh water, and not developing the typical test as 

 seen in most other groups of the foraminifera. As these are not pre- 

 served in the fossil state and are not usually recognizable in dried 

 material they do not have as much attention paid to them as is given 

 to the rest of the group. 



The modern classification is not in any sense a final one but is 

 given here for the purpose of students interested in the group. 

 Various attempts have been made by some authors to group together 

 genera which have a similar form ; thus Ammodiscus, which is piano- 

 spiral made of cemented sand grains, has been placed in the same 

 family as Spirillina, which has a somewhat similar form but with a 

 perforate calcareous test, and also Cornuspira, which although the 

 same form has a test calcareous and imperforate. To place in one 

 group dififerent species based solely on the shape of the test does 

 not seen to be a logical method, for, as in many other groups of 

 animals, parallelism is very marked. The structure of the test and 

 the material of which it is made seems to be a much better character 

 than mere form. As more is learned of the various species and 

 genera, it is very probable that the number of families will have to be 

 increased and somewhat new lines of classification adopted. A study 

 of the fossil occurrences of the dififerent genera is very necessary to 

 this as well as the structure of recent forms. For the sake of the 

 students in the group, a few of the descriptive terms commonly used 

 are here given, and a series of simple diagrams. 



One of the simplest arrangements of the chambers is that in such 

 coiled bilateral forms as Nonionina there are two distinct positions 



