Foraminifera from the North Sea, etc. 383 



by side, and cemented witli a mortar composed probably of the 

 finest dust of quartz, so that the whole test is of exquisite snowy 

 whiteness. . . ." 



As a matter of fact, the shell wall consists of two distinct 

 layers of spicules : an outer layer, in which the spicules are all 

 laid with their long axes parallel to the long axis of the test ; and 

 an inner layer of spicules laid with their long axes at right angles 

 to the outer layer. We thus get as close an approximation to 

 " woof and warp " as is possible with a rigid, non-flexile material, 

 and it is obvious that the strength of the test must be enormously 

 increased by the crossing of the two layers, as resistance to tensile 

 strain is given in two directions instead of one. 



The interstitial cement used by the animal is apparently a 

 very fine homogeneous mud, similar in colour and origin to that 

 employed by Marsipella spiralis and Bathysijphon filiformis (Sars). 

 Yery little of the cement is visible in the external layer, but the 

 spicules of the internal layer are deeply embedded in it, so that, as 

 a rule, only the middle portion of the spicule is visible when the 

 interior of tlie laid open test is viewed as an opaque object. This 

 led us, in 1909, to suppose that the interior layer consisted of 

 shorter spicules than the exterior layer. But the examination of 

 a large series of specimens has proved that identical spicules are 

 used for the exterior and interior walls. 



It is, moreover, noticeable that Technitdla leyumen rarely 

 employs broken spicules. Unlike Marsipella spiralis, which seems 

 to select fragments of approximately equal length, Technitella 

 legumen chooses minute but perfect acerate spicules of • 1-0 • 2 mm. 

 length, and thus secures material of practically constant standard 

 size. 



Sub-family Saccamminin^. 



Psammosphmra Schulze. 

 Psammosphiera ncstica sp. n. 



Test free, monothalamous, consisting of a polyhedral chamber 

 constructed almost entirely of sponge spicules, whole or frag- 

 mentary, neatly cemented together in a single layer, and with a 

 minimum quantity of ferruginous cement. The cement is confined 

 to the actual line of attachment between the edges of the spicules, 

 and does not extend over the outer or inner wall of the test. 

 There is no definite oral aperture. Average size, • 3-0 • 5 mm, 

 (chamber only). 



This beautiful and interesting form is not easily described, but 

 the illustrations will serve to demonstrate its extremely variable 

 (yet, within certain defined limits, constant) appearance, and the 

 method of its construction. 



