128 



PROTOZOA. 



together in loosely reticulate or vermiculate aggregations. The most 

 probable view of the relationships of this singular fossil is that it is an 



A B 



Fig. 32. — a, Fragment of limestone from the Ordovician rocks of Craighead, Girvan, of the 

 natural size, showing numerous exceptionally large masses of Girz>auella problematica ; B, 

 Section of a minute mass of Girvanella, enlarged about sixty times. (Original.) 



Arenaceous Foraminifer, allied to the recent genera Syringammina 

 and Hyperammina. 



The last group of the so-called "Imperforate" Foraminifera is 

 that of the Lituotidce, comprising an extensive series of arenaceous 

 types, in which the shell consists essentially of particles of coarse or 

 fine sand cemented together more or less firmly. In many cases 



the cement is calcareous, and though 

 the shell is usually imperforate, the 

 walls are in other cases pierced by 

 pseudopodial apertures. Sometimes 

 the test consists of purely calca- 

 reous particles embedded in a cal- 

 careous cement. In Lituola itself, 

 the type of the group (fig. 29, d\ 

 the test is generally crosier-shaped, 

 sometimes nautiloid, usually with a 

 rough exterior, and composed of 

 sand-grains agglutinated together. 

 The genus ranges from the Car- 

 boniferous to the present day. An 

 essentially Carboniferous type is 

 Fndothyra, in which the shell is 

 nautiloid, or resembles that of a 

 Rotalia in shape, and is found abundantly in the Mountain Lime- 

 stone of Britain. It forms in America entire beds of the Carbon- 

 iferous Limestone (fig. 33). Allied to Endothyra is the Liassic 



Fig. 33. — Section of Carboniferous Lime- 

 stone from Spergen Hill, Indiana, U.S., 

 showing numerous large-sized Foraininifera 

 {Endothyra) and a few oolitic grains mag- 

 nified. (Original.) 



