21. The costa has brown subquadrate marks and the exterior border has short brown streaks, which extend over the fringe. 22. There is a subquadrate purple-blackish blotch on the dorsum towards the base, margined above with brown suffusion. 23. "Tylonautilus " has a coiled shell with a subquadrate whorl section, evolutely coiled with all whorls showing. 24. The aperture is subquadrate , nacreous, smooth within, and has a groove indicating the place of the external keel. 25. A small cloudy subquadrate dark-grey spot is found beneath the fourth dot, sometimes connected indistinctly with the third. 26. Its shell has a subquadrate whorl section, flattended venter, and fine ribs that spring in bundles from large umbilical tubercles. 27. The rhachidian tooth has a subquadrate body with winged sides and a long triangular cusp with convex sides, which are serrated. 28. The forewings are brown, with the median fascia dark brown, subquadrate and broadly developed near the basal one-third. 29. In 2000, Michael Benton noted the existence of a robust ilium that has a back end that is subquadrate instead of rounded. 30. There is a roundish spot outlined with darker before the middle, and a subquadrate spot somewhat more distinctly outlined beyond the middle.
