Shell morphology. Measurements up to 3.5x2.2 mm, with 4 whorls; occasionally larger. General shape moderately high, with whorls distinctly flattened in their upper part. Base of body whorl also flattened. Surface of shell shows distinct, crowded growth lines and a veryfine spiralmicrosculpture all over. Shell material is moderately translucent. Aperture grossly oval, tending to be squarish in its lower part. Inner lip may be appresscd or leave a very reduced umbilical chink. Colour pattern. The colour pattern is fairly constant and includes one single tone ojreddish brown (tending to red on worn shells) on a tan to whitish background. This is commonly accompanied by opaque-white markings. Commonest pattern includes a series of flames below the suture (alternating with opaque-white patches), a similar row of brown and white patches at the periphery, and the remainder of the shell occupied by regularly-displayed dots or flecks extending down to the columella. Occasionally, the dots extend up to the suture, replacing the flames.

Radular morphology. The central tooth is characterized by subparallel anterior and posterior margins, and a rounded outline on each side.
The first pair of laterals terminate in a strong, stout conical cusp and bears 4 to 5 other similar cusps strongly decreasing in size towards the inner side. There is, moreover, an outermost cusp which is characteristically reduced in size. The next two pairs of laterals also terminate in a strong conical cusp, rather elongate in shape, but there are usually no more than 2-3 cusps on the inner side. These have also a reduced outermost cusp. The first 3 pairs of laterals are grossly equivalent in size, whereas the two next ones decrease in size and are tricuspid.
The marginals are imbricated in the first 4-5 rows. The first pair is smaller than the next and bears a digitation on its inner side. The pectinate structure is achieved by the 8th to 10th row.

T. petiti is best characterized by
(1) squarish shape of the aperture (i.e. subangular periphery of the last whorl);
(2) very monotonous one-tone polychromatism exclusively of dots and patches, never any oblique lines.
Radular morphology in this species is very like that in the T. pullus group. Maybe most characteristic is the elongate outline of 2nd and 3rd laterals.

This species has been found in scattered localities of continental Gulf of Guinea, from Gaboon to Togo. Its extension further west along the African coast is not documented. Specimens illustrated have been collected at low water mark on a tidal flat.