FORAMINIFERA. 



127 



is tubular, composed of arenaceous tubes, of which the sand-grains 

 may be loosely or firmly cemented together, and which may be free 

 or may be adherent along one side to foreign bodies. The tubular 

 test may be branched or radiate, or may simply be more or less 

 loosely coiled and contorted. One of the most remarkable recent 

 types of this group is Syringammina, in which the test is described 

 by Dr Brady as forming masses of branching, radiating tubes, arranged 

 in more or less distinct layers or tiers. In Hypera?nmina, again, the 

 test (fig. 31) has the form of a sandy tube, often of indefinite length, 



Fig. 31. — The winding tubular test of Hypcraimnina vagans, adherent on one side to a piece 

 of broken shell, a Initial chamber ; b General pseudopodial aperture. The figure is enlarged 

 fifteen diameters. Recent. (After H. B. Brady.) 



with the closed end commonly inflated so as to form a distinct 

 chamber, the pseudopodia being emitted from a general aperture at 

 the opposite end of the tube. The tube in this genus may be free, 

 or may be adherent to foreign bodies. 



The forms just mentioned throw light upon some very remarkable 

 fossils which occur in great numbers in certain of the Ordovician 

 limestones of Britain and North America, and which have been 

 described under the generic name of Girvanella ( = Strephochetus). 

 The fossils in question present themselves in the form of small 

 rounded or irregular nodules (fig. 32, a), which are sometimes so 

 abundant as to constitute a conspicuous element in the limestone. 

 When broken, these nodules show a distinctly concentric structure, 

 and when examined by means of thin sections (fig. 32, b), they are 

 found to consist of exceedingly minute circular tubes (about 1-45 

 millimetre in diameter), endlessly contorted and bent, and twisted 



