Shell white, acutely conical, with the anterior wall slightly, and the posterior wall strongly concave ; tip sharply recurved, acute, not spinal, directed backward in the middle line ; surface ornamented with about forty very slender radiating lines, fewer toward the apex with intercalary threads toward the margin ; concentric sculpture consisting of extremely delicate, irregularly disposed aggregations of the lines of growth, which now rise above and now fall below the general plane of the surface, giving it under a strong magnifier a curiously malleated appearance, between the radiating threads, nowhere exhibiting any uniform concentricity ; where the lines of growth cross the radiating threads they form fine overlapping scales closely appressed to the threads ; puncture ovate, pointed behind ; margin thickened, perfectly smooth ; septum triangular, inclined forward under the puncture which it almost entirely hides when viewed from below ; basal edge subcircular, Lon. 5.75 mm ; lat. 5.0 mm; alt. 3.0 mm. (Described by Dall as Puncturella)

Shell thin, small, about 7 mm. in length, conical, expanding rather abruptly toward the margin, height very variable, from 60% to 85%; of the length. Color a glossy oyster-white. Anterior half of the shell has straight sides, while the posterior half has concave sides. Apical whorls one and one half, smooth and highly polished. They lie at the summit of the shell, immediately behind the fissure and project markedly backwards instead of lying flat against the side of the shell as in certain other species. Fissure rounded in front and drawn backwards and upwards to a point in the shape of a tear drop. In very young specimens the surface of the shell is smooth. The same is true of adults so far as the area around the summit is concerned; the remainder of the adult shell however is sculptured with fine beaded radiating ribs. These, as they approach the margin, are augmented by finer intercalated ribs. Numerous extremely fine threads cross the shell, beading the ribs at the point of intersection and giving to the surface a peculiar delicately foliated appearance. Margin faintly crenulated. Interior of shell glossy. The radiating ribs of the outside are marked by translucent lines. Well down towards the margin a ridge is found, below which is the muscular sear. The septum is a shelf extending from side to side and down for a short distance. It divides the interior of the shell into two almost equal parts, the anterior being slightly smaller than the posterior. This beautiful species is rather rare. It is a deep sea form, living in depths ranging from 380 to .580 fathoms.

P. circularis is very closely related to P. borroi. See Remarks under this latter species. It resembles superficially P. profundi, but they can easily be separated: P. circularis is narrower near the top and it expands rather abruptly toward the margin, while P. profundi expands gradually from the top to the margin. The apical whorls in P. profundi are a little larger and lie slightly flattened against the posterior slope, while in P. circularis the apical whorls project markedly backward. In addition, the sculpture of P. profundi is more compact and extends over the entire shell below the apical whorls while in P. circularis the compact sculpture is limited to the basal area of the shell.

Range. Eastern Florida, Florida Keys, Cuba and south to Tobago Island.
Records. FLORIDA: off Fernandina, Albatross, station 2008 in 204 fathoms; off Tortugas, Blake, station 44 in 580 fathoms (both USNM). CUBA: off' Bahia de Cardenas, Atlantis, station 2903 in 580 fathoms; off Bahia de Santa Clara, Atlantis, station 2991 in 575 fathoms and station 2988 in 880 fathoms (all MCZ); off Cienfuegos, Atlantis, station 8388 in 1075 fathoms (Univ. of Habana). LESSER ANTILLES: Tobago Island (Dall 1927, p. 112).

This species differs in various details from Puncturella profundi Jeffreys, and is apparently nearer his P. granulosa from the Norwegian coast and the Porcupine Expedition (60-292 fathoms). That species has no concentric sculpture, however, and has not been fully described as far as is known to me. It belongs, with the preceding and with Puncturella Cooperi Carpenter, from the northwest coast of America, in the genus Fissurisepta of Seguenza. This differs in most specimens by having no props to the septum, a character, however, which is not constant even in the same species, as in a large series of Alaskan forms I have found every transition from fully developed props to none at all, in specimens which differed in no other character. Hence, while it may be a permanent feature in some species, I doubt if it is yet sufficiently established to be safely used as a generic character.