Original Description Test biserial, usually consisting of 5-6 pairs of chambers; periphery in initial portion entire, later indented; chambers slightly inflated, barrel-shaped to subglobular, increasing regularly in size as added with the exception of chambers of the final pair which increase sharply in size and constitute 1/2-1/3 of test length; chambers of final pair somewhat flattened, reniform, overlapping; chambers of the penultimate pair partly or completely overlapped; chambers of final pair are deflected in one side thus forming a depression between final pair and earlier part of test; final pair of chambers is nearly twice as wide as long and often wider than the length of the test; sutures distinctly depressed, slightly oblique in regard to test axis; wall with discontinuous, delicate costae; primary aperture interiomarginal, a high arch; gerontic specimens with one additional pair of chambers, globular, lying in normal surface to the earlier part of test, and equal in size to the remainder of the test. Specimens included among this species may differ to some extent in test length, in size and shape of the last pair of chambers as well as in degree of its deflection from the axis of test. Size: Etymology: Extra details from original publication Variability. - Specimens included among this species may differ to some extent in test length, in size and shape of the last pair of chambers as well as in degree of its deflection from the axis of test.
Remarks. - The position of the last pair of chambers not in the plane of the other part of the test distinguishes the new species from all species of genus Heterohelix hitherto described. H. vistulaensis sp. n. is similar to H. pulchra (BROTZEN) in having two reniform terminal chambers but differs in (1) the development of the older part of the test, (2) the size of the ulti- mate .pair of chambers compared with the size of the whole test, (3) the position of the last pair of chambers not in the test axis, (4) smaller test/and (5) test ornamentation.