From Fensome et al., 2019:
Amphorosphaeridium multibrevum, Davey, 1969c, p.33–34, pl.3, figs.5–6; pl.4, fig.1; text-fig.1, no.3.
Holotype: Davey, 1969c, pl.3, fig.5.
Age: Campanian–Maastrichtian.

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Original description: [Davey, 1969]:

Diagnosis:
Central body subspherical, wall fibrous and pitted.
Processes numerous, four, rarely three, per plate area; hollow, tubiform and spinous distally. They are relatively short (approximately one-quarter central body diameter), of constant length but variable width. Apical and antapical processes not very distinctive.
Archaeopyle typically present.

Description:
The structure of the processes is similar to that of the processes of A. fenestratum except that they are shorter and may be joined proximally. Distally the processes are spinous, the spines on one side of each process typically being longer than those of the other side (fig. 1, no. 3). The apical and antapical processes are similar in height to the normal processes and are, thus, rather difficult to distinguish. The antapical process is slightly larger than the surrounding processes whereas the apical process is considerably broader and more complex. The cingulum is discernible on some specimens and is delimited by two parallel rows of processes.

Dimensions:
Central body diameter: Range: 47(58.1)73 μm (holotype: 54x57 μm).
Process length: Range: 12(14.0)18 μm (holotype: 13 μm). No. of specimens: 10.