Genus OENOPOTA Morch, 1852
Type species: Fusus pleurotomarius Couthouy, 1838, subsequent designation Dall, 1918.
We follow Powell (1966) and Bartsch (1941) and regard Lora as a substitute for Defrancia, the type of which is D. pagoda, which species to us seems to be close to Philbertia as Glibert (1954) supposed.
Synonyms:
Propebeta Iredale, 1918, type species Murex turricuta Montaeu. 1803. original designation
Turritoma Bartsch, 1941, type species Turritoma exquisita Bartsch, 1941, original designation. (Not Turritoma Ulrich & Scofield, 1897).
Turritomella Bartsch, 1941a, a new name for Turritoma Bartsch, 1941.
Nodotoma Bartsch, 1941, type species Pleurotoma impressa Mdrch, 1869.
Funitoma Bartsch, 1941, type species F. areta Bartsch, 1941, original designation.
Cestoma Bartsch, 1941, type species Funitoma (Cestoma) eurybia Bartsch, 1941, original
designation.
Granotoma Bartsch, 1941, type species Bela krausei Dall, 1886, original designation.
Nematoma Bartsch, 1941, type species N. hokkaidoensis Bartsch, 1941, original designation.
Curtitoma Bartsch, 1941, type species C. Hecuba Bartsch, 1941, original designation.
Venustoma Bartsch, 1941, type species V. harucoa Bartsch, 1941, original designation.
Canetoma Bartsch, 1941, type species C. tersa Bartsch, 1941, original designation.
Belalora Powell, 1951, type species B. thielei Powell, 1951, original designation.
Lorabela Powell, 1951, type species Bela peiseneeri Strebel, 1908, original designation. Having examined Bartsch's type material in USNM and also having some experience of the variation of arctic species of Oenopota, we cannot accept any of the genera proposed by Bartsch (1941). We are also convinced that if Powell had seen such species as O. tenuicostata, O. elegans, O. declivis and O. pyramidalis, which show all transitions from sinuated to nonsinuated outer lip, even within the species, he would never have proposed his genera. He also misinterpreted the larval shell of Belalora and considered 1.5 postlarval whorls as belonging to the larval shell.
Even if the species enumerated here are variable, everyone who has been in contact with arctic shallow-water material of the group will know that their variability is small compared with what appears in arctic forms. The variable physical conditions of the arctic area and the strong tendency for a species there to be split into isolated populations, in combination with the direct development, are factors strongly promoting high variation.
The genus as treated here is certainly not homogeneous, but its division into groups certainly does not follow the outlines drawn up by Bartsch (1941) and Powell (1966): Oenopota convexigyra goes into a group by itself, O. ovalis into another group and finally, the remaining species into one group.
The species of Oenopota are not very easy to separate as the large degree of variation tends to hide the limits of the species, but the following remarks may perhaps make separation easier: O. convexigyra is more slender than any other species; it has sinuated axial ribs, or better, incremental lines; the whorls are very slowly increasing and the spiral sculpture very regular. O. tenuicostata has a sculpture of sinuated axial ribs, a smooth rounded larval shell and a very broad and well-defined, slightly-excavated callous deposit on the body whorl.
O. elegans also has sinuous axial ribs, but the shell is much more slender and the larval shell has some strong spiral keels.
O. dictyophora has much the same outlines as O. tenuicostata and also a smooth, rounded larval shell, but the axial ribs are not sinuous, and run straight from the suture to the periphery where they are distinctly angulated and go on straight downwards. Also the callus of the parietal wall differs in being much less developed and more narrow.
O. ovalis has a short rounded aperture, poorly developed siphonal canal, smooth rounded larval shell and almost straight axial ribs.
O. scalaris is the biggest species. The shell is usually white or greyish white. The subsutural zone is well defined and usually rather flat but the whorls are well and evenly rounded below it. The outline is less cylindrical or ovate than in any other species of the genus, but instead rather rhombic.
O. violacea has a very poorly developed subsutural zone, which is strongly sloping and almost unnoticeably merges with the main part of the whorl. The sculpture is most variable but usually a few spiral cords are dominant. The larval shell is rather pointed and upturned and has some low spiral ribs.
O. turricula has very strong axial sculpture of solid, straight, broad and high ribs. The larval shell is high and upturned. The whorls are strongly shouldered. This is a shallow water species. O. graphica has strongly shouldered whorls, a sharp sculpture, a low aperture and straight or very slightly curved axial ribs which are strongly angulated at the periphery.
O. trevelliana has rather ovate outlines, a not very well defined subsutural zone, a rather low and flattened larval shell and a not very heavy sculpture.
O. bergensis has distinctly shouldered whorls, a rather low larval shell, cylindrical whorls and a distinct siphonal canal.
