Emarginula tuberculosa Libassi, 1859 Tuberculate Emarginula
Distribution: Georgia, Florida, Texas; West Indies to Brazil. Size: 12 to 18 mm.
Description: Color opaque to buff white, interior of shell polished with exterior sculpture showing through; shell cap shaped; elevated, height about 2/3 length; shell distinctly sculptured with primary ribs radiating from apex and alternating secondary ribs originating away from apex; concentric cords cross over the shell, creating nodules where they intersect and giving a cancellate appearance; anal fasciole long, becoming wader at the base, produced by closely set arched lamellae; fissure longer than wide, about 1/6 the length of anal fasciole.
Habitat: Encountered throughout its range at depths from 10 to 1170 m (33 to 3838 ft). In Texas recorded from the FGB.
Remarks: Shell variable in strength and sculpture; variability is thought to be attributed to factors other than geographic range. See Perez-Farfante
(1947).

This species reaches a large size, up to 18 mm. in length. The shell is highly sculptured, elevated, the height being about two thirds the length, with the anterior slope strongly convex and the posterior slope straight or concave. Apical whorls one and one halt*. These whorls are sometimes reduced to a small pointed hook. The position of the apical whorls varies from one high on the shell, close to but a little below the summit and immediately in front of the posterior end. to one near the base and projecting beyond the posterior end. Anal fasciole with numerous, rather closely-set, arched lamellae which are frequently in greater numbers than the concentric cords that cross the shell. Fissure rather wide and about one-sixth the length of the anterior slope. Sculpture consists of numerous raised primary ribs radiating from the apex to the margin. Secondary ribs, which start some distance from the apex, alternate with them. Sometimes very line riblets that originate lower down than the secondary ribs are intercalated between the primary and secondary ribs. Numerous concentric cords cross the surface of the shell forming thickened nodules where they intersect the ribs. These cords divide the spaces between the ribs into more or less square pits. Sometimes two very short chalky white lines are found in the square pits. Color opaque white or buff. Margin finely and strongly crenulated by the termination of the ribs. Interior of shell highly polished, the sculpture of the outside showing through as radiating and concentric translucent lines. The anal fasciole is marked inside by a grooved callus. Length 12-18 mm; Width 9-13 mm; Height: 6-11 mm

6. Emarginula tuberculosa Libassi, 1859. With numerous ribs, every fourth rib slightly larger at the margin. Length, 13 mm; height, 7 mm. A species of wide distribution, known in the eastern Pacific from Isabela Island, Galápagos Islands, to Octavia Rocks and Port Utria, Colombia, in 80 to 180 m; also in the western and eastern Atlantic.

Emarginula tuberculosa is rather common throughout its range in the Western Atlantic, having been found in depths of from 33 to 450 fathoms. This species shows a variation in the thickness of the shell and in the strength of the sculpture. Specimens from some localities are much thinner and more delicate than those from other places. In the former the shell is sculptured by fine radiating and concentric threads while in heavy specimens there are raised ribs and strong cords. This variation has no geographical significance since all forms varying from thin to heavy are found in adjacent localities throughout the range of this species. Monterosato in 1892, discussed Jeffreys' misidentifieation of E. tuberculosa Libassi as E. compressa Cantraine. He presents the characters that distinguish the true compressa, proposing for it a new genus, Agariste.

EASTERN ATLANTIC : off Portugal and Azores. WESTERN ATLANTIC : Georgia, Florida and south through the West Indies to Brasil.