Caecum brasilicum, DE FOLIN, 1874

Raines, Bret, 2023, Caecidae (Mollusca: Gastropoda) from late Miocene exposures of the “ Imperial ” Formation in Riverside County, California, PaleoBios 40 (1928), pp. 1-11 : 7-8

CAECUM BRASILICUM DE FOLIN, 1874

FIG. 6A–C

Caecum brasilicum de Folin, 1874: 212, pl. 9, fig. 6, 19 syntypes MNHN-IM-2000-25785, Brazil .

Caecum brasilicum — Kisch, 1959: 39; Mello & Maestrati, 1986: 151, fig. 6; Rios, 1994: 56, pl. 18, fig. 1994; Gomes & Absalão, 1996: 515, figs. 1–3; Oliveira & Almeida, 1999: 2, fig. 4; Costa et al. 2021: 84, fig. 2A–C.

Original diagnosis — "Testa tubularia, subcylindrica, satis arcuata, crystallina, nitidissima; annulis XX-XXIV, quadratis, satis prominentibus et latis, interstitiis latis separatis, cincta; striae longitudinales annulos et interstitia decussantes; interdum annuli primi acuti vel subrotundati, haud longitudinaliter strigis decussati; aperturam versus contracta; apertura saepe marginata, parum declivis; septum ungulatum, interdum submucronatum vel subacutum, margine laterali undulato. Operculum bruneo-flavum concavum, suturae distinctae, anfractus subconvexi." de Folin (1874: 212).

English translation — "Shell tubular, subcylindrical, quite curved, crystal like, shiny; 20-24 annular rings, squarish, quite prominent and broad, separated by wide intervals, encircled; longitudinal striae covering rings and intervals; sometimes rings are first sharp or somewhat rounded, without lengthwise striae; distally spaced,often widening toward the aperture, somewhat sloping; septum hoof-like, sometimes submucronatus or subacute, lateral margin wavy. Operculum brownish-yellow convex, sutures distinct, whorls subconvex."

Referred Specimens —LACMIP 43085.10 (1 specimen); LACMIP 43085.11 (7 specimens); LACMIP 43085.12 (66 specimens).

Occurrence — Known only from immediately above and below the Thylacodes beds near the base of section SC 3 in Super Creek, Riverside County, California .

Description — Protoconch and subadult stages not observed. Teleoconch average size for genus [Tol: 1.80– 2.05 mm], tubular, strongly and regularly arched [Larc: 0.50–0.60 mm; Arc: 0.20–0.25 mm], subcylindrical with increase in diameter from posterior to aperture, creamy white. Axial sculpture consists of 20–22 rings, which may vary from triangular in posterior region becoming squared toward aperture. Axial interspaces about the same width as rings. Posterior [Dpe: 0.32–0.36 mm] with squared shoulder. Septum mucronate, flattened to re- cessed. Mucro with projected rounded point, positioned along dorsal margin. Aperture [Da: 0.46–0.52 mm] with slight downturn, mildly constricted. No varix. Lip smooth, weakly developed, with slightly deflected peristome.

Discussion — As pointed out by de Folin (1874: 212) and Gomes & Absalão (1996: 527), Caecum brasilicum will often feature two types of rings (triangular and quadrangular) on a single specimen.

Figures

Figure 6A–C. Caecum brasilicum: A–B, LACMIP 43085.7, LACMIP 43085.8, profile views; C, LACMIP 43085.9, ventral view. Scale bar=500μm