Diagnosis.– Hendersonia with test wall flexure developed on all the chambers of the test, distinct trend of pore alignment in the proximity of the sutures, costae thickenings in the central part of the test, adjacent to the ‘zigzag’ suture and sometimes with crater-like pores.

Description.– Test is biserial throughout. Proloculus is small (8.1-11.7 µm). There are 12 to 14 globular to subglobular chambers, which increase gradually and moderately in size as added. Earlier chambers are globular in shape, those of the adult portion of the test are subglobular to subrectangular in shape as seen in lateral view (Pl.3, Figs 3, 6, 10); chamber shape is consistently globular to subglobular in shape in edge view (Pl. 3, Figs 4, 5, 8, 9). Sutures are distinct and depressed, straight to slightly oblique to the test axis of growth. Periphery is subacute due to the development of a test wall flexure, which results in the duplication of the test wall in the chamber
periphery region (Pl. 3, Figs 8, 9). The test wall flexure is developed on all the chambers of the test, sometimes forming a rim-like structure around the test (Pl. 3, Figs 1,2, 5, 6, 10). Aperture is a low to medium high arch at the base of the last chamber. Two short, symmetrically developed flanges, which can be imperforate to microperforate, border the aperture on the two lateral sides (Pl. 3, Figs 4,6). The oldest portion of the test (apical region) can be smooth in some specimens (Pl. 3, Fig. 9). There is a distinct pustulose periapertural area at the top of the chambers (Pl.3, Figs 3-6, 8), which can be absent in more or less eroded specimens (Pl. 3, Fig. 9). Most of the test surface is covered with thick costae, which can be linear (Pl. 3, Figs 6, 7, 10) or with undulated sides (Pl. 3, Fig. 3); their thickness range is between 3.1 and 5.3 µm, being thicker on the inner part of the chambers, in the proximity of the central ‘zigzag’  suture (Pl. 3, Figs 3, 6, 10). Test wall is calcitic, hyaline and finely perforate; pores can be simple (Pl. 3, Figs 6-8,10) or situated in the center of a crater-like structure (Fig.6, Pl. 3, Figs 3-4). Pore diameter ranges between 1.1 and 2.4 µm. There is a distinct trend of pore alignment around the chambers and in the proximity of the sutures on the earlier chambers of the test (Pl. 3, Figs 3, 6, 7, 10).

Remarks.– Hendersonia  jerseyensis n. sp. differs from H. hendersoni nov. sp. by the development of a test wall flexure on all the chambers of the test, thicker costae (3.1-5.3 µm when compared to 2.3-3.1µm), ornamentation thickenings on in the proximity of the central ‘zigzag’ suture on the earlier chambers and the trend to develop pore alignment around the chambers on those of the earlier portion of the test. This species differs from H. carinata (Cushman, 1938) by the pore alignment trend around the chambers of the early part of the test and the absence of the compressed appearance of the last chamber in edge view. Worth mentioning, the development of pores situated in the central part of a crater-like structure is a characteristic of Hendersonia jerseyensis n. sp. among the other species of the genus; the taxonomic significance of these structures was recently demonstrated in the case of the hedbergellid species Liuella falklandica Georgescu,2008 from the Lower Campanian sediments of the Falkland Plateau (Georgescu, 2008).

Phylogenetic relationships.– Hendersonia  jerseyensis n. sp. evolved from H. carinata (Cushman, 1938). Apparently it became extinct leaving no descendants (Fig. 4).

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