Adult shell is of medium height for the genus, varying from 88.9mm (paratype 6) to 99.5mm (paratype 1). The shell is solid and high spired. The protoconch consists of approx. 5 smooth, weakly convex whorls with a distinct suture. The initial whorl is lowest and often eroded. By the third protococh whorl a distinct keel is present above the suture, continuing to the teleoconch whorls. The teleoconch of some individuals is marked by a distinct and in some cases jagged growth line. By the second or third teleoconch whorl, weak spiral cords commence with very narrow interstices of 0.2mm to 0.3mm. There are approx. 13 to 16 spiral cords, of which the subsutural cord, comprised of a series of distinct vertical slots, is most prominent. The spiral cords become obsolete near the centre of the ventral surface of the body whorl. The body whorl, combined with posterior canal, comprises approx. 60% of the length of the shell and is generally smooth except for 35 to 45 fine spiral cords on the anterior third of the dorsal surface. The columellar callus is indistinct or obsolete. The outer lip is slightly thickened internally only near the posterior canal. The outer lip margin is followed by a distinct but superficial callus. The posterior canal is reduced to a shallow notch, curved dorsally. The outer lip is comprised of a convex thickened section, extending from the posterior notch for approx. 10mm to 12mm, ending in a distinct indentation forming the first of four to six (but mostly five) evenly spaced short digits. The posterior canal is deep, long and twisted to the left when viewed ventrally. The protoconch is white and subsequent whorls have a subsutural narrow band of chestnut brown, obsolete by the penultimate whorl. Spire and body whorls are traversed by vertical brown parallel lines, which may be wavy or zigzagging, becoming wider on the dorsum of the body whorl. The ventral surface of the body whorl is sparsely striated. The outer lip callus is lined with darker brown. The columellar callus and aperture are white. Thin and almost transparent periostracum is present.

Rostellariella lorenzi sp. nov. most closely resembles R. delicatula, a widespread species in the northern Indian Ocean. The most obvious conchological difference is the colour pattern of R. lorenzi sp. nov. The tan vertical stripes are discernible even in dead or eroded shells and the outer lip callus is a dark brown, whereas for R. delicatula it is orange. The outer lip dentation and structure of the two species are significantly different: Rostellariella delicatula does not have the posterior convex projection and predigital notch present on the outer lip of R. lorenzi sp. nov. Most specimens of R. delicatula have four digits (De Turck et al, 1999). Melvill and Standen (1905)
cite a range of 3 - 5 digits for R. delicatula, but show the following ratios and therefore also indicate the predominant number as 4 digits:
3 digits 1: 75 with 4 digits
5 digits 1: 25 with 4 digits
Of the 24 adult specimens of R. lorenzi sp. nov. examined, 19 had five digits and 5 had
four. The posterior canal is longer in R. lorenzi sp. nov. and is always twisted to the left when
viewed ventrally. There is a distinct transverse striation on the teleoconch whorls of R. lorenzi, especially below the suture, whereas the surface of the later whorls of R. delicatula
is smooth.The anterior columellar half of the last whorl is rather coarsely ribbed in R. delicatula, whereas in R. lorenzi the ribbing is very dense and fine.
The other species within the genus Rostellariella is R. martini (Marrat, 1877) from the South China Sea, Philippines and northern Borneo areas (Dc Turck et al, 1999), geographically separated from R. lorenzi sp. nov. This much larger species can readily be differentiated also by its more inflated, lighter shell, shorter lip digits, orange-tan colour and a longer, straight posterior canal.

Indonesia, Arafura Sea, bordered by the Indonesian island of Timor to the west, Tanimbar and Aru Islands to the north and the Australian territorial boundary to the south. Rostellariella lorenzi sp. nov. is taken by Indonesian fishermen working throughout the Arafura Sea, at a depth range from 200 to 400 metres. The habitat was described as muddy sand and coarse shell rubble. Several dead specimens were filled with fine grey mud consistent with the anecdotal information gathered from the fishermen.