Description. Shell large sized for genus, length up to 26.1 mm, width 13.8 mm (holotype), specimens mature no less than 18.0 mm in length, shape stout, thick, heavy, spire squat, short, low profile, functional tubes somewhat short, recurved, flange large, thick, widely flaring, continuous from one whorl to the next, pits deep, wide, closely set, especially prominent on varices. Intritacalx relatively thick, chalky with distinct growth lines. Color mostly off white with some brown between cords and on both siphonal canal and functional tubes.
Spire high with an unknown protoconch and teleoconch up to 4.5 whorls. Last whorl spiral morphology with IP, P1, s1, P2, P3, P4, P5, s5, P6, ADP, MP and ABP. Aperture ovate, columellar wall thick, projecting, extending away from previous whorl. Apertural denticles consisting of small Dl, D2 and D3 always split, D4 & D5 more subtle, but distinct, angled toward axis, anterior end blunt, rounded, nearly flat at anterior end. Siphonal canal short, 22 % of total shell length (holotype), very broad, ventrally sealed, slightly convex near previous whorl, cord and final varices intersection concave, acutely pointed.

Tripterotyphis galapagosensis n. sp. is easily distinguishable on the basis of its large size, weight, different spiral morphology and the locality to which it is endemic. This species exceeds 18.0 mm at maturity, has a thickness and very heavy weight unlike other species and contains only a s1 cord unlike other species of this genus, with additional secondary cords, or in the case of T. jamesmacleani, which lacks secondary cords. This species was thought to be potentially new by D'Attilio as was stated by Finet (1985: 19) and additionally was suspect to the senior author (Wiedrick, 2012: 92) in the review of Panamic specimens analyzed. Although unillustrated, a specimen recorded as attaining a length of 23.6 mm from the Islas Galapagos, Ecuador (Pisor, 2008: 108) conforms with other specimens reviewed in this study and is here assumed to be a specimen of this species. Specimens of large size have historically been noted as coming from the Islas Galapagos (D'Attilio, 1979: 51; D'Attilio & Hertz, 1984: 52; Wiedrick, 2012: 92), a notable morphological characteristic, as well as being geographically isolated to this eastern Pacific archipelago. The radula of this species was illustrated by D'Attilio & Hertz (1988: fig. 4) and morphological features are distinctly different from those of the most allied species, Tripterotyphis lowei in addition to T. lowei having a much thinner shell, narrower functional canal, a more acute siphonal canal, far less distinct spiral cords, a narrow aperture, having s5 and lacking ABP. Unfigured specimens from Islas Galapagos (Finet, 1985: 19; Kaiser, 2001: 5; Garrigues, 2020: 41), with size measurements omitted, are here regarded as T. galapagosensis n. sp. based on their locality, and the fact that no specimens of T. lowei have been detected from this locality.

Type locality. Isla Floreana, Islas Galapagos, Ecuador, 1° 15'00" S, 90° 19'58" W, under coral at 10- 25 m, 15 Feb 1988, collected by Donald R. Shasky.
Distribution. Known only from the Islas Galapagos, Ecuador, intertidal to 27 m.