Shell elongate-conic, white; nuclear whorls 2,5 , forming a depressed, helicoid spire, with the axis at right angles to that of the following whorls, in the first of which they are about one third immersed; postnuclear whorls 10, high between the sutures, with the sides flattened; axial sculpture of low, almost vertical ribs, of which 18 appear on the early whorls and 20 on the last whorl; interspaces shallow, nearly twice as wide as the ribs, marked with about 12, indistinct, irregularly spaced, spiral series of pits; periphery of last whorl rounded, marked by a stronger spiral series of pits, below which the ribs fade out; base moderately long, marked with fine, incised spiral lines; aperture subquadrate, outer lip thin, showing the external sculpture within; columella nearly straight. The type measures: length, 5.5 mm; diameter, 1.4 mm.
Holotype: No. 754 (Calif. Acad. Sci. Paleo. Type Coll.), from Loc. 27,228 (C.A.S.), dredged in from 3 to 9 fms. off Taboga Island, Panama. L. G. Hertlein collector. A second specimen was dredged at the same locality and two young specimens at Loc. 27,229 (C.A.S.), in Bahia Honda, Panama.
In the key given by Dall & Bartsch to the west coast species in the subgenus Pyrgiscus, the new species garthi would follow macbridei from which it is easily distinguished by its less slender form and fewer axial ribs.
This species is named for Mr. John S. Garth, who accompanied the expedition, as collector of Lepidoptera and as musician.