REPORT OK THE FORAMINIFERA. 
267 
of the rays serving as apertures. Walls coarsely arenaceous, very firmly cemented ; 
exterior rough, internal surface smooth. Dimensions very variable, ranging from about 
ijth to -frds inch (3 to 17 mm.) from point to point. 
Rhabdanimina abyssorum was one of several new species of Foraminifera enumerated 
by the late Prof. Michael Sars in his list of animals dredged in deep water off the coast of 
Norway. Of these and many other marine invertebrata discovered by the lamented 
Norwegian naturalist, no description was published, and their identification is due to the 
kindness of his son Prof. G-. 0. Sars in distributing type specimens. 
Some idea of the variety of form assumed by the test may be gathered from PI. XXI., 
but it would require a much longer array of figures to illustrate fully the polymorphic 
tendencies of the species. Its salient morphological features are described by Dr. 
Carpenter 1 in the following terms : — 
“ What is most remarkable, is the geometrical regularity of its form, which is typically 
triradiate [figs. 1, 2], the rays diverging at equal angles from the central cavity, and each 
being a tube with an orifice at its extremity. Not unfrequently, however, it is quadri- 
rcidiate [figs. 3, 4], the rays diverging at right angles ; and occasionally a fifth ray 
presents itself, its radiation, however, being on a different plane [fig. 7]. The three rays 
are normally of equal length ; but one of them is sometimes shorter than the other two ; 
and when this is the case, the angle between the long rays increases at the expense of the 
other two, so that the long rays lie more nearly in a straight line [fig. 8]. Sometimes the 
place of the third ray is indicated only by a little knob ; and then the two long rays have 
very nearly the same direction. We are thus led to forms in which there is no vestige of 
a third ray, 2 but merely a single straight tube, with an orifice at each end ; and the length 
of this, which often exceeds half an inch, taken in connection with the abundance in which 
it presents itself in dredgings in which the triradiate forms are rare, seems to preclude 
the idea that these long single rods are broken rays of the latter.” 
Little need be added to the foregoing clear exposition, which, though written on the 
basis of specimens collected from a comparatively limited area of the North Atlantic, is for 
the most part equally applicable to those obtained from other parts of the world. It may 
be remarked, however, that in the quadri-radiate tests the arms are not always arranged at 
right angles (see fig. 6) ; and in the five-rayed specimens, the tubular arms though often 
irregular, as shown in fig. 7, are nevertheless sometimes disposed on one plane, as in figs. 
5 and 11. 
Occasionally ramose tubes, like fig. 9, are met with in localities where Rhabdammince 
abound. Such specimens probably belong to an allied species referred to by Dr. Carpenter 
in his notes on some of the Foraminifera procured on the “ Lightning” Expedition, under 
1 The Microscope and its Revelations, 6tli Ed., 1881, p. 562.— The references in brackets apply to figures in PI. 
XXI. of the present Memoir. 
2 The Rhabdammina discreta of the present Report, PI. XXII. figs. 7-10 
