500 FORAMINIFERA I LAGENIDA. 



382. Lagenida. — Passing-on, now, to the Vitreous series of 

 Foraminifera, we revert in the first instance to those simple 

 Monothalamous or Single-chambered shells, some of which repeat 

 in a very curious manner the lowest forms already described. 

 Thus Spirillina has a minute, spirally-convoluted, undivided 

 tube, resembling that of Cornuspira (Plate xv., fig. 1), but having 

 its wall somewhat coarsely perforated by numerous apertures for 

 the emission of Pseudopodia. So in Lagena we seem to have the 

 representative of Grromia ; not only, however, is the membranous 

 'test' of the latter replaced by a minutely-porous Shell, but its 

 wide mouth is narrowed and prolonged into a tubular neck 

 (fig. 9), giving to the shell the form of a microscopic flask ; this 

 neck terminates in an everted lip, which is marked with radiating 

 furrows. A mouth of this kind is a distinctive character of a 

 large group of Polythalamous shells, of which each single chamber 

 bears a more or less close resemblance to the simple Lagena, and of 

 which, like it, the external surface generally presents some kind 

 of ornamentation, which may have the form either of longitudinal 

 ribs or of pointed tubercles. Thus the shell of Nodosavia (fig. 10) 

 is obviously made up of a succession of Lageniform chambers, the 

 neck of each being received into the cavity of that which succeeds 

 it ; whilst in CHstellaria (fig. 11) we have a similar succession 

 of chambers, presenting the characteristic radiate aperture, and 

 often longitudinally ribbed, disposed in a Nautiloid spiral. Be- 

 tween Nodosaria and Cristellaria, moreover, there is such a gra- 

 dational series of connecting forms as shows that no essential 

 difference exists between these two types, which must be combined 

 into one genus Nodosarina ; and it is a fact of no little interest 

 that these varietal forms, of which many are to be met with on 

 our own shores, but which are more abundant on those of the 

 Mediterranean, and especially of the Adriatic, can be traced back- 

 wards in Geological time even as far as the New Red Sandstone 

 period. In another Genus, Polymorpliina, we find the shell to 

 be made up of Lageniform chambers arranged in a double series, 

 alternating with each other on the two sides of a rectilinear axis 

 (fig. 13) ; here again, the forms of the individual chambers, and 

 the mode in which they are set one upon another, vary in such a 

 manner as to give rise to very marked differences in the general 

 configuration of the shell, which are indicated by the name it bears. 

 — All those Foraminifera, whether Simple or Composite, whose 

 Shells are made up of Lageniform chambers, may be very natu- 

 rally associated under one Family Lagenida ; notwithstanding that 

 they were distributed by D'Orbigny (according to the differences of 

 their plans of growth) under four different Orders. 



383. Globigerinida. — Returning once again to the simple Mono- 

 thalamous condition, we have in Orbulina — a minute spherical 

 shell that presents itself in greater or less abundance in Deep Sea 

 dredgings from almost every region of the globe — a globular 



