Specimens from the West Atlantic are indistinguishable from West African material on conchological grounds, but the radula has one or two conspicuous sharp denticles on the inside of the first (inner) marginal instead of one to three inconspicuous bumps, and both the lateral and rachidian teeth have fewer denticles. Whether these differences are constant, indicating a small degree of differentiation, is impossible to determine now, as so little material has so far been studied. The taxonomic significance of the horny jaws has not been investigated.

The distribution and continuous transition between morphs leave no doubt that a single somewhat variable species is involved in our concept of O. sulcata. The nominate form is small and stout, with a thick outer lip, and occurs in 1000-2500 m. (Specimens labelled fischeri by Locard are indistinguishable from typical sulcata.) Specimens from deeper water are larger, the shell is lighter, and have a reflected but thin outer lip. This is the form called abyssorum which, in the eastern Atlantic dominates at a depth of 3000-4500 m. In the western Atlantic the variation is similar, with solid, small specimens as shallow as 338 m, and the larger, thin-shelled abyssorum form in deep water. In the southwestern Atlantic, abyssal specimens have a taller spire than in the northwestern Atlantic, and have a very fragile shell. Specimens called "watsoni" have a moderately light shell but otherwise correspond more or less to that tall spired form. The form described as O. umbilicata has an umbilicus, like abyssorum, and is as solid and heavy as sulcata, but cannot be separated.
Three other names introduced for specimens of Oocorys from the Indian Ocean may be synonyms: O. sulcata var. indica Smith, 1906, O. weberi Schepman, 1909 and O. schepmani Turner. 1948. We have, however, not examined the type material.
The protoconch is multispiral, with reticulate sculpture, and planktotrophic larval development can be inferred. It resembles that of Laubierina, but is smaller, with lower spire, and raised spiral cords extending into the umbilical region (Figs 1920, 1922).

From southwest of Ireland and off New England southwards, to the Azores, the Caribbean and the Gulf of Mexico (Bayer 1971, Quinn 1980, and material in USNM), off western and southwestern Africa (Bayer 1971 and material in MNHN), and off northeastern Brazil (material in MNHN). Outside the Atlantic, O. sulcata has been recorded from off southern Africa (Kilburn 1975), the Indian Ocean (Smith 1906, and material listed above), from Indonesia (Schepman 1909) and the southwestern Pacific. It is a bathyal and abyssal species. The deepest records are 5062 m in the Caribbean Sea and 5073 m in the Vema Fracture Zone (Mid-Atlantic), and there are repeated occurences in 350-500 m in the Caribbean and the Gulf of Guinea. Off Europe however it never occurs more shallow than 1000 m.

Oocorys sulcata seems to have a continuous distribution in about 350-5000 m throughout the Atlantic, Indian and Pacific Oceans, i.e., apparently throughout the world's temperate and tropical oceans (other than the Mediterranean). Specimens are confirmed as occurring from southwest of Ireland and off New England south to Brazil and off southern East Africa, in the Indian Ocean, in Indonesia, around Japan, around New Zealand, Australia, the New Caledonian region, Vanuatu and Fiji, i.e., wherever intensive deep-sea sampling has been carried out. The holotype of O. rotunda Dall, from the Gulf of Panama, eastern Pacific, is likely to be a further specimen of O. sulcata.

The name Benthodolium abyssorum was provided for very thin-shelled specimens with a thin, narrow inner lip (which therefore reveals a narrow false umbilicus) and a thin, only weakly flared outer lip, and with sculpture of very narrow, widely spaced spiral cords. These specimens came from deep water (holotype from 4042 m). The name Oocorys sulcata Fischer (1883) was based on thicker-shelled specimens with wider spiral cords, a thicker and wider inner lip that hides the umbilicus in most specimens, and a more thickened, more strongly flared outer lip forming a true varix. These specimens came from shallower water (holotype from 2235 m; but this form occurs as shallow as c. 350 m). All specimens have an anterior siphonal notch in the dorso-ventral plane and no anterior canal (in the sense of protruding below the base of the outer lip), the base of the columella is deviated sharply to the left, and they have a fairly uniform shape, with evenly rounded, well inflated whorls, and no axial sculpture other than growth lines. Bouchet & Waren (1993) concluded that these forms intergrade completely, and that these and many of the other nominal species proposed in Oocorys refer to one biological species. The larger amount of material available now makes it clear that this synonymy is correct, and that the range of variation is still greater than Bouchet & Waren (1993) thought. I have no doubt that O. sulcata is an extremely wide-ranging, quite variable species, forming thinner shells with much narrower spiral cords in deeper water than it does in shallower water. A large lot in MNHN from the Gulf of Mexico, LGL Cruise 3.MMS.C5, 26°57'N, 89°3FW, in 2486-2523 m (17 dried, 20 in alcohol), includes a range of shape and sculpture nicely intermediate between the sulcata and abyssorum forms. The holotype of O. rotunda is a little taller and narrower than most other specimens assigned to O. sulcata, but can be matched among the large MNHN Atlantic collections of O. sulcata. Larger (H 53.9 mm) specimens from Fiji in BORDAU 1 samples closely resemble the holotype in shape, and occur with standard specimens of O. sulcata. There seems little doubt that O. rotunda is yet another synonym of O. sulcata, extending its range to the eastern Pacific. The type material of O. elongata Schepman (= O. schepmani Turner) does not have any characters differentiating it from O. sulcata. Some Indian Ocean specimens, such as the types of O. weberi and Eudolium aulacodes, have more prominent and more widely spaced spiral cords than most Atlantic and western Pacific specimens I have seen, but some of the Indian Ocean specimens identified by Bouchet & Waren (1993) as O. sulcata (e.g., Madagascar, chalutage 109, 1200 m, 22°17'S, 42°56'E, one specimen; MD32 REUNION stn CP 105, 1740-1850 m, 20°47,S, 55°04'E, one specimen) and a few from New Caledonia and Vanuatu (e.g., Loyalty Basin, BIOGEOCAL stn CP 214) are almost as strongly sculptured as the holotype of O. weberi, and in my opinion this name also was based on extreme specimens of O. sulcata. The holotype of Eudolium aulacodes also seems to be a very extreme, coarsely and sparsely sculptured specimen of O. sulcata, and was referred to Oocorys by both Kilburn (1986) and Marshall (1992).