Caecum semicinctum de Folin, 1867

Figures 66 A–E, 67A–I, 68A–B, 128C

Caecum semicinctum de Folin, 1867a: 42, 17 syntypes MNHN-IM-2000-4587, Panama.

Caecum semicinctum — Kisch, 1959a: 33.

Material examined. In addition to the type material the following lots were examined. NHMLAC: LACM 1972 - 63.90, Cano Island, Puntarenas Prov., Costa Rica, 8–13 m, 12 sh . SBMNH: SBMNH 452504, Bahia Santiago, Colima, Mexico, 27–40 m, 20 sh ; SBMNH 452521, Bahia de Culebra, Guanacaste, Costa Rica, 13–23 m, 10 sh ; SBMNH 619852, Isla Danzante, Baja California Sur, Mexico, 60–90 m, 1 sh; SBMNH 620486, Isla Danzante, NE end, Baja California Sur, Mexico, 60–90 m, 1 sh; SBMNH 621646, ICP-03-012, Coiba National Park, Veraguas, Panama, 5–19 m, 9 sh ; SBMNH 621649, Isla de Coiba, Veraguas, Panama, 1 sh; SBMNH 622497, Bahia Santiago, Colima, Mexico, 13 m, 4 sh .

Original diagnosis. “Testa elongata, cylindrica, paulo arcuata, subcornea, fulgente, annulis rotundatis parum prominentibus cincta, (interstitiis minimis) deinde levi; aperturam versus annulis rotundatis ornata; apertura haud declivi, simpliciter marginata; septo mamillato, obtusissimo, subspirali, annulum rotundatum super septi planum fingente; margine laterali arcuato, convexo; operculo?” de Folin (1867a: 42).

Description. Protoconch and teleoconch I unknown. Teleoconch II short, smooth (Fig. 67A, B), transition to teleoconch III marked by slight, incised axial line (Fig. 67A). Teleoconch III about four times length of teleoconch II, smooth (Fig. 67B), transition to teleoconch IV marked by slight incised axial line (Fig. 67C). Teleoconch IV smooth with occasional axial growth lines (Fig. 67D), transition to teleoconch V marked by suture (Figs. 67C, E). Teleoconch V (last growth stage) small for genus [Tol 1.61–1.93 mm], tubular, rather thick, moderately and regularly arched [Larc: 0.57–0.62 mm; Arc: 0.14–0.19 mm], subcylindrical, creamy white (Figs. 66 A–B, 67I). Axial sculpture of 3–4 rounded annuli, equally spaced on posterior end, 4–6 raised rings on apertural end (Figs. 67 H–I). Surface smooth with numerous axial growth lines (Fig. 67G). Posterior [Dpe: 0.35–0.36 mm] with thick edge, rounded shoulder (Fig. 66C). Septum mucronate, slightly recessed (Fig. 66C). Mucro with low rounded point, positioned on dorsal margin (Fig. 66C). Aperture [Da: 0.41–0.47 mm] thick, with slight flare followed by abrupt constriction (Fig. 67I). No varix. Lip smooth, with deflected peristome (Fig. 66C). Periostracum thin, smooth, yellowish (Fig. 66A). Operculum thin, light brown; exterior surface with 6–8 concentric rings (Fig. 66E). Conceptual reconstruction of growth stages shown in Fig. 68A.

Distribution and Habitat. From Isla Danzante, Baja California Sur, Mexico to Panama Bay, Panama. Intertidal to 90 m. Uncommon on coarse sand and rocky substrates.

Remarks. The type material of Caecum semicinctum is comprised of both subadult and adult specimens (MNHN-IM-2000-4587, Fig. 66D). Neither Keen nor Lightfoot ever mentioned this species. Caecum semicinctum is somewhat uncommon, but easily recognizable.