REPOET ON THE EORAMINIFERA. 
439 
Family VII. LAGENIDAE. 
The Lagenihf form an extensive family of vitreous Foraminifera, characterised 
primarily by the calcareous and finely perforated nature of the test, and its terminal aperture. 
In the young condition the test is thin and transparent ; but in mature specimens it 
is more commonly thickened by the continued deposit of calcareous shell-substance, either 
evenly over the whole surface, or in the form of exogenous growths, such as tubercles, 
spines, costae, or reticulated lines. 
The test is either monothalamous or polythalamous ; when monotlialamous it forms 
a simple chamber with a central orifice, when polythalamous it consists of a number of 
similar chambers or segments, joined one to the other in single series, usually in such a manner 
that the anterior wall of the first segment forms the posterior wall of the second, and so on. 
The characters of the aperture vary in the several genera, but its typical aspect may 
be said to be that of a rounded orifice, either with an everted edge or divided at the margin 
by radiating fissures. In some genera — frequently in Lagena and Nodosaria , almost 
invariably in Uvigerina — the aperture is situated in a more or less extended tubular neck, 
terminating in a pliialine lip. 
The primitive or monothalamous condition of the test is exemplified in the genus Lagena, 
which consists typically of a single rounded or compressed chamber. A number of rounded 
Lagena-Vke chambers, joined end to end in a straight or curved line, form the test of 
the genus Nodosaria ; and a straight test, similarly constructed, but of flattened segments 
compactly fitted together, that of Lingulina. Frondicularia exhibits similar features to 
the latter, but the shell is still more flattened, and the successive segments are embracing 
or equitant. The curved Nodosarice with central aperture, pass by insensible gradations 
into the somewhat shorter forms with marginal orifice which compose the genus Mar- 
ginulina ; and these into the corresponding flattened varieties which constitute Vaginulina,. 
In Vaginulina the test is more or less curved, and the segments are obliquely set : 
the increased obliquity of the early chambers leads to the production of the partially 
spiral test of the crosier-shaped modifications of Cristellaria, and these in turn to the 
typical or helicoid forms of that genus. There remain two other subordinate genera 
belonging to this series, namely, Rliabdogonimn , the shell of which differs from that of 
the true Nodosarice in its trilateral or quadrilateral contour and angular margins ; and 
Rimulina, a subtype of Vaginulina , distinguished chiefly by the nature of its aperture. 
In Cristellaria the convolutions are equilateral, and disposed in one plane ; but there 
are other groups in which the chambers, though more or less spiral, are arranged round an 
elongated axis. Of these the genus Polymorphina comprises the less regular forms, and 
Uvigerina those which are more definitely spiral, the distinction between the two 
depending partly upon the characters of their respective apertures. 
