Shell ashy white, elongated, thin, six-whorled. Nucleus translucent, smooth, polished, of about one and a half whorls; whorls slightly convex, appressed to the suture behind them, connected by three continuous fin-like varices which in descending the spire make about half a revolution around it; these varices on the upper whorls were extended backward into a little wing-like point with dentate edges; on the last whorl the lines of growth indicate that the thin margin was rounded, parallel with the whorl. Transverse sculpture of fine growth-lines, and on the last two whorls at the periphery three short little narrow pinched-up riblets between the varices; spiral sculpture of fine rather faint striae and wider undulations, hardly visible except on the varices; of these there are nine or ten on the last varix. Aperture elongate-oval, internally white, thickened, smooth; canal rather long, open, bent back. Max. lon. of shell, 17.0 mm; of last whorl, 13.5 mm; of aperture, 5.0 mm; max. lat. of aperture, 3.0 mm; of shell, 8.0 mm.
NOT FIGURED.

This is the smallest of all known Pterynotus species (maximum length 20 mm), and its shell is thin, translucent, and fusiform. The spire is moderately high, consisting of one and one-half polished nuclear whorls canted opposite to the cant of the remaining four weakly convex postnuclear whorls. The suture is distinct but not impressed. The body whorl is broadly fusoid. The aperture is lenticular, with a sharp, narrow anal sulcus, this bounded on each side by a node. The outer apertural lip is erect. The columellar lip is adherent. The siphonal canal is moderate in length, narrowly open, and distally recurved.
The body whorl bears three winglike varices, each of which generally follows the contours of the shell. Each "wing" is appressed above to a varical wing on the preceding whorl, drawn outward and upward at the shoulder margin into a sharp point, as in P. vespertilio, extending anteriorly no further than the base of the body, gently undulate on its ventral surface, reflecting low spiral cords on the dorsal surface, and laminate. The dorsal surface is given an undulate character by a series of low spiral cords, each cord extending into a recurved point on the margin of the wing. Axial sculpture consists of numerous faint growth striae. Spiral sculpture, in addition to the low cords mentioned above, consists of innumerable scratches crossing the growth striae to impart to the shell surface a microscopically cross-hatched effect. Shell color is uniform white.

This species agrees more nearly with the Indo-Pacific species by having three intervarical ribs, while the Atlantic species hitherto known have only one. It is, however, more nearly related to Pterynotus tristichus than to any hitherto described, as far as I have been able to ascertain. The body of the shell is not unlike that of P. cordismei Watson, figured in the Challenger Report, but the present species has none of the semitubular spines which give the Australian shell the look of a Typhis.

United States. Off St. Augustine, Florida.