NOTES ON RETICULARIAN RHIZOFODA. 289 



which the inferior aperture is single and relatively small, but is 

 supplemented by conspicuous orifices on the superior or 

 spiral surface of the test — type, Gl. rubra. 



Bat, in addition to the spiral Glohigerbw^ or rather those 

 that appear so externally, there are certain spherical forms 

 constituting the reputed genus Orbtilina. Without entering 

 into minutiae, Orhulina may be defined as a minute, thin- 

 walled, Globigerine shell enveloped in a large globular final 

 chamber. Examples are not wanting, amongst other genera, 

 of varieties leading up to similar conditions, but in none is 

 the phenomenon so completely developed. In my previous 

 paper I have indicated the fact, suggesting, by its uniformity, 

 a gei^ral law, that when a Foraminifer forms an abnormally 

 large segment, growth is arrested and no more chambers are 

 produced. Amongst spiral Foraminifera Cymhalopora hul- 

 loides affords the most familiar example of a species with a 

 balloon-shaped final segment, but the same peculiarity is 

 developed in a less degree in certain modifications of i)/5corii?«a 

 and Ptihinulma. All these forms have another character in 

 common with Orhulina, namely, a double series of perfora- 

 tions ; that is to say, the wall of the inflated chamber has 

 two sorts of orifices, differing in size, the one set numerous 

 and nnifoimly very minute, "the other uniformly large and 

 fewer in number. 



The question arises whether the characters exhibited by 

 these Orbuline forms are to be regarded as of mere varietal 

 significance or as sufficient to warrant subgeneric or generic 

 distinction. The reply seems to be, that the close affinity to 

 Glohigerina is best expressed and zoological convenience is 

 best served by accepting Orbulina as a subgeneric type of 

 that genus. 



Glohigerina {Orhulina) universa, d'Orbigny ('Foram., 

 Cuba,' p. 35, pi. 1, fig. 1) — is figured by d'Orbigny, William- 

 son and others as a small spherical shell of yellowish hue, 

 with a neat, round, general aperture in addition to the per- 

 forations that have been already alluded to ; but Pourtales, 

 Williamson, and Carpenter have all dwelt on the fact that 

 this large orifice only appears in a minority of the specimens 

 found. I am inclined to go a good deal further and, though 

 not prepared to say that it does not sometimes exist, I 

 believe it to be very rarely indeed that a fresh shell possesses 

 what has any claim to be considered a general aperture. 

 After looking over thousands of specimens I have not been 

 able to find one from which a drawing like those of the text- 

 books could be made. In dredged specimens large orifices 



