MANUAL OF NATURAL HISTORY. 373 



II CLASS.— FOBAMINIFERS (Forairiinifera), 



Animal bursiform, simple, gelatinous, without 

 appreciable organization, but secreting a delicate, 

 many-celled, internal, calcareous skeleton, into the 

 cells of which the animal can retract ; mouth central, 

 surrounded by retractile, tentacular processes, which 

 constantly vary in form, and which serve for swim- 

 ming and crawling. 



1. Family. — Straight-Foraminifers (Vaginulidse) 



Shell many-celled, with the cells placed end 

 to end in a single series in a straight or 

 slightly curved form. 



2. Family. — Alternating -Foraminifers (Textu- 



lariidse). Shell many-celled, with the cells 

 disposed alternately in two or three parallel 

 series, but without forming a regular spiral. 



3. Family. — Spiral- Foraminifers (Discorbidse). 



Shell many-celled, with the cells arranged in 

 a single series, but forming a regular spiral, 

 which is discoidal or turriculate. 



4. Family. — Imbricated-Foraminifers (Miliolidse). 



Shell with the cells variously clustered and 

 imbricate, and each rolled round a common 

 axis ; aperture usually furnished with an 

 appendage. 



5. Family. — Compound -Foraminifers (Orbiculi- 



nidae). Shell with the cells divided into se- 

 veral smaller cavities by small tubes, or by 

 partitions. 



