Shell of medium to large size for the genus, sturdy but not massive, umbilicate, nacreous within, suture deeply channeled, whorls and base rounded. Nucleus of 1.5 flattened whorls with a single carination, 4 postnuclear whorls. Spiral sculpture on early whorls of 3 cords, the uppermost consisting of a row of projecting, rounded beads, the other 2 unbeaded until reaching the final whorl and a hali. Weak, beaded interstitial cords emerge next to the upper 2 of the original 3 cords on the final whorl. The suture is laid on a strong cord that delimits the base, but does not strongly project. The basal cord is exposed by a slightly descending suture on the final whorl. Base sculptured with 6 major and 1 minor cord, 1 bordering the umbilicus and 2 descending deep within. Axial sculpture of fine growth lamellae over entire surface, apparent chiefly in the interspaces between cords but not directly on the beaded surfaces. Lip not thickened, growing edge sharp. Color brick red, with scattered white flecking along the spiral cords. Height, 6.0, diameter, 6.9 mm.

Arene ferruginosa differs from all Eastern Pacific and Western Atlantic species known to me in having only the uppermost cord beaded on the early whorls. Of the 11 eastern Pacific species it is the only one characteristically found in moderately deep water: the other species occur at depths of 20 fathoms or less. It is one of the few species of Arene not having a greatly thickened mature lip. In this feature it is similar to A. bairdii (Dall, 1889), a brick red Caribbean species occurring at similar depths. The latter species does not show the peculiar beading feature of the early ribs of A. ferruginosa. The specimens from Wenman Island, Galapagos Islands (Figs. 28-29), and Cocos Island, Costa Rica, reach only 3 mm in height but are evidently mature because the suture descends on the final whorl. Dwarf populations apparently occur at these localities. The name means rust-colored, with reference to the brick red coloration.

Type Locality: South of White Friars, Mexico, 17° 30' 50" N, 101° 29' 55" W, 25 fathoms on rocky bottom, R/V Velero III station 264-34, 2 March 1934, 1 specimen. Type Material: Holotype: LACM-AHF 1393.
Referred Material:. Specimens are represented from the following AHF bottom sample stations: 332, Bahia Honda, Panama, 30-50 fathoms, 34 specimens, mostly fragmentary and in subfossil condition; 330, Chatham Bay, Cocos Island, Costa Rica, 47 fathoms, 2 specimens; 430, Wenman Island, Galapagos Islands, Ecuador, 150 fathoms, 3 specimens.