1883.] 



On Syringammina. 



157 



condition than they are, were it not that the disintegrated por- 

 tions formed a layer of sand in the bottom of the bottle, partially 

 embedding the larger pieces. Owing to this want of cohesion it 

 has been found impossible to prepare thin sections of any part of 

 the test. 



The inferior aspect of the specimen, represented in PI. 2, fig. 1, is 

 entirely a fractured surface, and is probably something approaching a 

 median section ; but it is much too uneven to show any regularity of 

 structure, except at some points near the periphery. The only portion 

 remaining of what was originally the exterior of the test is shown in the 

 side view, fig. 3, at the point marked a. The convex or "superior" 

 aspect of the specimen, as it stands on the plate, exhibits chiefly the 

 open ends of the transversly-broken tubes. 



The different portions of the structure examined in detail reveal 

 little beyond what may be realised at the first glance. 



The "inferior" surface of the specimen displays somewhat more 

 regularity in the radial arrangement of the tubes than could be made 

 apparent in the drawing, owing to the unevenness of the fracture. 

 The organic centre appears to have been broken away, and it is 

 impossible to say whether there has been originally any true nucleus, 

 in the shape of a well-defined primordial chamber. The central 

 portions, so far as they are left, consist of a network of branching and 

 often contorted tubes, of somewhat smaller diameter than those of the 

 exterior, and less regularly disposed (PI. 3, fig. 8). 



Nearer the periphery the system of tubes takes a distinctly radial 

 character, and in a favourable section appears divided into con- 

 centric layers or tiers of gradually increasing depth (fig. 6). The 

 concentric " partitions " exhibited in the radial section of the test, 

 fig. 6, d.d., are not, like the "labyrinthic layers" of Parlzeria, con- 

 tinuous septa of cancellated structure, but are formed by lateral 

 branches, given off at intervals, which unite so as to produce a more 

 or less regular network (fig. 7). As nearly as can be made out, 

 there may have been ten or eleven such reticulated " partitions," at 

 intervals varying from inch (1'26 millims.) near the centre, to 

 y 1 ^ inch (2*5 millims.) near the periphery. 



As already stated the tubes are not of uniform diameter, those near 

 the centre measuring sometimes no more than inch (05 millim.), 

 whilst near the exterior they often exceed inch (1 millim.), the 

 average diameter being about ^ inch (0*735 millim.). The external 

 surface is granular, but in the dry condition it is tolerably smooth ; 

 the interior is smooth and well finished. The internal cavity whether 

 of the radial tubes or the branches is continuous, exhibiting neither 

 constrictions, septa, nor labyrinthic subdivision. The thickness of the 

 walls is about inch (0*125 millim.). 



The peripheral ends of the tubes are rounded, and closed by an 



