SEM images of recently acquired specimens of Globigerina siakensisLeRoy, 1939, from near its type locality in Indonesia and other areas verify previous claims about the spinosity of the test wall and confirm assignment of the species to Paragloborotalia. Furthermore, they show that the species has straight intercameral sutures on the spiral side of the test.
Paragloborotalia siakensis has previously been synonymized with Globorotalia mayeriCushman and Ellisor, 1939. Backscatter electron, high-vacuum SEM images of Gl. mayeri show that the holotype has curved spiral-side intercameral sutures and apparently lacks spinosity. The absence of the latter feature, however, cannot be confirmed because the holotype is poorly preserved, the single paratype belongs to a different species, and topotypes are unavailable.
The straight spiral-side intercameral sutures in P. siakensis and the curved ones in the Gl. mayeri holotype argue against the synonymy of both species, certainly for those using a typological species approach. For those applying an assemblage-based concept, synonymy is demonstrated if specimens with curved and straight spiral-side intercameral sutures occur in single homogeneous assemblages, preferably from the type localities of both species, and are connected by intermediate morphologies. Unfortunately, neither the type sample of Gl. mayeri nor its washed residue is preserved, and there is no possibility of resampling the relevant interval. However, assemblages of P. siakensis from its type area, Java, and Trinidad are clearly devoid of specimens with Gl. mayeri-like suture patterns, providing sufficient reason to retain the name P. siakensis. If the wall of Gl. mayeri is not spinose, the species most likely is closely related to, or a senior synonym of, Globorotalia partimlabiataRuggieri and Sprovieri, 1970.