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IX . — Note on a New Type of Foraminifera of the Family 
Chilostomellidse. 
By Henry B. Brady, LL.D., F.R.S 
{Read 15 tli October , 1890.) 
One of the most curious and interesting features of the Foraminifera, 
often an element of difficulty to the student, is the tendency of the 
modifications of the types composing the larger groups to run in 
parallel isomorphous series. Thus, if the entire Class be divided 
roughly, as it has sometimes been, into three Orders, comprising re- 
spectively the forms characterized by porcellanous, arenaceous, and 
hyaline tests, species with tests presenting the same general conforma- 
tion and similar arrangement of chambers may in some cases be found 
in each of the three series. We have examples of three isomorphous 
forms — that is to say, of porcellanous, arenaceous, and hyaline genera 
possessing similar morphological characters — in Cornuspira, Ammo- 
discus , and Spirillina ; in Aheolina, Loftusia, and Fusulina ; in 
Nubecularia (N. tibia and N. divaricata), Beophax, and Nodosaria ; 
. Hauerina 1 Trochammina ) Cristellaria 1 # 
a uc m p ener0 pH s ^ 9 Jlaplopliragmium $ ’ an Nonionina j J au 
a considerable number of instances might be added of two such 
isomorphous genera. The same tendency exhibits itself even in the 
smaller groups, most remarkably, perhaps, in the Botaliidse, of which 
the species of three or four genera may be arraDged in parallel columns, 
in more or less closely isomorphous series. The phenomenon, in fact, 
is so common as almost to suggest a general law. 
It is somewhat remarkable, however, that hitherto we have been 
unacquainted with any forms of the hyaline and arenaceous classes 
corresponding at all closely in general structure to the commonest of 
all the porcellanous types, those namely of the Sub-family Miliolininm . 
The characters of the Sub-family are summarized as follows in the 
scheme of classification appended to the report on the ‘ Challenger ’ 
Foraminifera,* — “ Chambers, two in each convolution, coiled on an 
elongated axis, either symmetrically in a single plane, or inequilater- 
ally. Aperture alternately at either end of the shell” — the entire 
family, of course, being characterized by the imperforate and (normally) 
porcellanous and calcareous investment. Turning to the perforate 
or hyaline series, the only approach to corresponding structure is to 
be found in the Chilostomellidse. In the genus Chilostomella the 
segments may be said to be two in each convolution, inasmuch as 
each does not completely inclose that preceding it ; they follow each 
other alternately from the two ends of the test, and the aperture is at 
* ‘Report ou the Foraminifera of the Challenger Expedition,’ 1884, p. 61. 
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