The shell is large for the genus (maximum length 40 mm) and stoutly fusiform. The spire is moderately high, consisting of two and one-half nuclear whorls and six convex to weakly shouldered postnuclear whorls. The suture is impressed. The body whorl is moderately globose and fusoid. The aperture is subcircular, with no discernible anal sulcus. The outer apertural lip is finely dentate at its margin, weakly undulate to smooth within. The columellar lip is primarily adherent above, detached and strongly erect below. The siphonal canal is long, narrowly open to the right, and dorsally recurved.
The body whorl bears seven or eight well-developed varices. Additional axial sculpture consists of numerous scabrous laminae. Spiral sculpture consists of eight major cords, five on the body and three on the canal; the cords are tripartite, consisting of a strong medial ridge flanked on each side by a weaker one. An evident unsculptured gap is apparent between the body and the canal. Where the cords intersect the varices, short, recurved, open, foliated spines are developed. The leading edge of the varix is richly fimbriate.
Shell color is off-white, with a medium-brown band on the shoulder, the white coloration persisting on the leading edges of the varices, the spaces between the cords as they surmount the varices, and the area between the body and the canal; the intervarical space and the spines are generally suffused with a deep fleshy pink. The aperture is porcelaneous white.

Murex humilis Broderip, 1833, was described with Santa Elena, Ecuador, as type locality. The species was first figured by SOWERBY (1834). The description and figure are of a shell with a globose body whorl, a moderately elevated spire of about 5 whorls, and a long, nearly straight canal. Varices are fimbriated along the leading edges and are intersected by spiral cords. The intersections give rise to spines that terminate sharply and are spirally recurved. Below the body whorl, on the upper part of the canal, is a wide band where the axial and spiral sculpture is greatly subdued. Anteriorly on the canal are 3 rows of sharp recurved spines that rise from the terminations of spiral cords at the leading edges of obsolete canals. Based on the large number of specimens examined, further details may be added. The nucleus is conical, of 3 globose whorls, the first small, the other 2 increasing regularly. The tip is immersed. The entire nucleus is covered with microscopic granules. The first postnuclear whorl has 8 low axial ribs that extend over the third nuclear whorl and are attached to it for the lower 1/3 of its height.
The varices are formed by the terminations of successive growth stages. In mature specimens, the thin outer layer of each growth stage is reinforced with successive layers of shell material deposited on the inner surface. The layers are slightly separated along the terminal edge. Each growth stage is begun below the last layer of the preceding one. Thus, the leading edge of each varix is exposed as an expanded frilly cross section of the shell wall. Although all specimens examined began postnuclear growth with 8 varices per whorl, some increased the number with growth and some decreased. The range for the number of varices on the adult body whorl was 6 to 9, with 56% of the specimens having 8. There are 5 major cords on the body whorl, 2 on the spire, and 3 anteriorly on the canal. Each major cord is marked by 9 to 14 small grooves and resembles a bundle of fine threads. At the termination, these smaller threads broaden axially and end successively from the outside in toward the heaviest central thread. The entire spine is recurved spirally as much as 1800 and terminates sharply. In some cases, a secondary thread separates and recurves to form a second smaller spine. Between the heaviest cord at the shoulder and the suture is a minor cord with minor spines. The 3 rows of spines on the anterior one-half of the siphonal canal occurred on 81% of the specimens. The other 19% had only 2 rows. In this case, a third obsolete row was apparent on some specimens. On others, a third row was present on earlier growth stages but became obsolete before the final varix. Three rows of spines on the anterior part of the canal seems to be normal for this species.
Murex norrisii Reeve, 1845, was compared in the original description with M. humilis. The only significant difference noted was several rows of very small, sharp spines in the nearly smooth region on the canal anterior to the aperture. Reeve's illustration shows these. All specimens of M. humilis showed 3 to 5 small cords in this region terminating as small straight spines. Most of these were broken off; but some of them were intact and were as much as 2 mm in length. Comparable spines were also noted on the other 2 species. This is probably a characteristic of the "humilis" group in the sense it is used by VOKES (1970).

Specimens from Panama are typical. Shells of specimens from the Guaymas, Mexico, region are less robust and more strongly shouldered, lack the pinkish-purple suffusion, and have a less globose body. Shells of specimens from the Manzanillo, Mexico, area are dwarfed, lack strong coloration, and are lacking much of the scabrous lamination of typical specimens.

Northern Gulf of California (eastern side) to Panama, the Galapagos Islands, and Ecuador.