322 
THE VOYAGE OF H.M.S. CHALLENGER. 
n n fr equently assuming oval, compressed, subangular, or altogether irregular forms. Colour 
brown ; shell- wall very thin, composed of light-coloured sand-grains, fitted together 
accurately and firmly with reddish-brown cement. Diameter from -^th to -^th inch 
(O' 4 to 1*3 mm.). 
Thurammina papillata is a very variable species, and the foregoing summary 
of its typical characters, is based upon average specimens, such as that represented in 
PL XXXVI. fig. 7. In order to arrive at a correct estimate of its morphological range, 
some of the more - important deviations from the typical structure may be briefly 
described. 
Normally the test is free ; nevertheless in localities where the species is abundant 
small specimens are not unfrequently met with in the sessile condition shown in fig. 11, 
and in these the shape is more or less modified to suit its altered external relations. 
Occasionally two or three spheres are found attached to each other, as in fig. 15. Such 
specimens appear to be the result of the adherent growth of several independent tests, 
which do not assume a corporate existence as a single polythalamous organism ; or, in 
other words, the polythalamous condition depends upon mere superficial adhesion, and 
not upon the division of the sarco le into segments connected with each other by proper 
stolons, and forming a corresponding shelly investment. 
Sometimes, though very rarely, on breaking a sphere, a second smaller chamber is 
found in the interior. An example of this sort is represented in fig. 12, and primordial 
chambers from other specimens, with the papillae projecting in the form of tubes of 
various lengths, are shown in figs. 13 and 14. The occurrence of such specimens is ex- 
ceedingly interesting as a point of analogy between Thurammina and Orhulina. 
The external contour of the test is influenced by other circumstances besides its 
occasional adherent growth, and the most common departures from the normal spherical 
form are either in the direction of mere asymmetry (fig. 10), or of elongation in one 
direction, so as to produce an ovate test (fig. 8), the latter being more especially notice- 
able in large specimens. These remarks apply mainly to recent tests. The Jurassic 
examples of the species present much greater diversity of contour, and comparatively few 
of them show any degree of external symmetry. 
The oral papillae vary in number from half a dozen to a hundred or more, and it by 
no means follows that the largest test has the most numerous apertures ; often quite the 
reverse is the case. They are sometimes placed with a certain degree of regularity as to 
their distance apart (fig. 7), and in rare instances are arranged in lines (figs. 9, 10); but 
in a general way they are scattered over the surface of the test, apparently without law 
or order. In some specimens, especially amongst those of medium or small size, one of 
the papillae is more or less elongated, so as to form a tubular neck, like that of an 
ectosolenian Lagena, as in figs. 9, 10, 11, and 15. The papillae are probably, as a rule, 
