Shell (Figure D-E) small (to 5.7 mm), very thin, fusiform/pagodiform, with low (spire angle 76-79°) stepped spire and concave sutural ramp with posteriorly deflected carina along its periphery. Protoconch (Figure1) tall (900mu), conical, increasing in diameter from « 225 to 930 mu in two evenly rounded whorls, with fine granules arranged in spiral rows. Transition to teleoconch distinct, marked by appearance of sinuate axial grown lines, strong shoulder, and two spiral cords below shoulder. Teleoconch up to three sharply shouldered, convex whorls. Suture adpressed, subsutural area sloping to posteriorly deflected, thickened carina at shoulder. Spiral sculpture of low spiral cords with narrower interstices, seven weak cords between suture and shoulder, c.45 cords between shoulder and siphonal canal, 15 cords on siphonal canal slightly wider than on shell periphery. Axial sculpture limited to fine prosocline growth lines strongly sinuous between shoulder and suture (corresponding to anal sinus). Last whorl high, 0.76 of SL. Anal sinus wide, deep (cone-eighth whorl). Aperture large (AL/SL = 0.46), wide (AL/AW = 1.8), oval, deflected from coiling axis by 28°, with broad, convex parietal region, short, weakly sinuous columella, and long, wide, open, axial siphonal canal. Outer lip thin, fragile, smooth. Shell colour yellowish white, with darker, caramel-coloured bands along shoulder and between shell periphery and distal siphonal canal. Entire teleoconch surface finely granulose.
Radula of holotype (Figure J-L) with simple, hypodermic marginal teeth. Teeth small, c.50 [am long (1.7% of AL and 1.1% of SL), straight. Tooth canal opening laterally at tooth base, opening roughly triangular, large. Apical opening lateral, long, narrow, oval. No barbs or blade. Tooth with short, blunt spur above basal opening (Figure K, s). Teeth connected to vestigial subradular membrane by wide and very thin ligament

Pleurotomella petiti may be easily distinguished from all congeners by its characteristic pagodiform shell with a sharply angled shoulder and posteriorly deflected carina. It somewhat resembles P. annulata, which has a laterally directed carina at the shoulder, as well as an anterior carina, and multiple raised spiral cords between the suture and shoulder and along the last whorl that are absent in P. petiti.