FORAMINIFEBA OF THE ATLANTIC OCEAN, 37 



absence of ceineut at the point of jiiucture. This opening, however, appears to be 

 merely accidental and is not present in the majority of specimens. The cement 

 used is not ferruginous, but appears to consist of very fine homogeneous mud. It 

 is absorbent and very easily broken up, and is no doubt very porous, thus serving 

 for the passage of the protoplasmic extensions. 



The specimens vary considerably in size and shape, but the most usual form has 

 a length about twice its breadth. 



Average length, 0.4-0.0 mm.; breadth, 0. 25-0. 85 mm. 



Distribution. — This species was originally described froiii tlie 

 deep water in the gully off Burghead, in the Moray Firtli, (wld- 

 seeJcer, haul 73, 35 fathoms, ami haul 7791, in 55 nieter.s. From 

 the Clare Island Survey the authors record single specimens from 

 four stations and two from a fifth, depths varying from 3 to 15 

 fathoms. The further record is from two stations off the west of 

 Scotland, each in 30 fathoms, and a single specimen at each station. 



PSAMMOSPHAERA RUSTICA Heron-Allen and Earland. 



Plate 9, figs. 3, 4; plate 10, figs. 2-4. 



Psammosphaera rustica Heron-Allen and Earland, Journ. RoJ^ Micr. Soc, 

 1912, p. 383, pi. 5, figs. 3, 4; pi. 6, figs. 2-4. 



The original description is as follows: 



Test free, monothalamous, consisting of a polyhedral chamber constructed almost 

 entirely of sponge spicules, whole or fragmentary, neatly cemented together in a 

 single layer, and with a minimum cjuantity of ferruginous cement. The cement is 

 confined to the actual line of attachment between the edges of the spicules, and does 

 not extend OA'er the outer or inner wall of the test. There is no definite oral aperture. 

 Average size, 0.3-0.5 mm. (chambers only). 



Hardly any two specimens exhibit an identical shape or external appearance. 

 This diversity is due to the methods of construction and material employed. Ap- 

 parent method of construction is to select a number of long slender spicules often 

 2 or 3 mm. or more in length. These are placed like tent poles at various angles 

 about 0.5 mm. apart, forming a rough open-work figure inclosing a central space be- 

 tween the points of intersection of the poles. The open spaces in the wall are then 

 filled in with shorter fragments of spicules carefully selected for length, so as just 

 to fill the required space. The animal thus secures the nearest possible approach 

 to a spherical chamber obtainable with the material employed, the salient angles 

 being the points where two or more of the ''tent poles" join. The long spicules 

 employed as "tent-poles" project irregularly all over the surface of the test in per- 

 fect specimens, and probably serve a secondary purpose as catamaran spars in sup- 

 porting the animal in the surface layer of ooze. They are, however, very fragile, and 

 are frequently more or less damaged, if not destroyed, in the process of cleaning the 

 dredged material. 



The internal cavity of the test is quite devoid of projecting spicules and is not coated 

 with cement. 



As a rule, spicules only are employed in the construction of the test, but occasionally 

 a minute grain of sand or flake of mica is used to close the little corner space where 

 two or more "tent-pole " spicules meet at an acute angle. Still more rarely this angu- 

 lar space is left unclosed, thus constituting an aperture to the test. The presence of 

 such apertures must, however, be regarded as abnormal. 



(composite specimens were found with two to five individuals in an irregular mass. 

 The only union between such specimens is that they have used in common one or 

 more of the same long spicules. Usually the groups are irregular, but in one of the 



