Mexistrophia obsoleta Thompson, 2011

Original Description

"Mexistrophia obsoleta new species

Diagnosis: Distinguished by obese pupiform shape, obsolescent color pattern, and sculpture in which upper ends of ribs do not crenulate suture and ribs become obsolete or are absent on lower two whorls. Peristome white, relatively narrow, lacking noticeable callus within.

Description: Shell (Figures 7-10) obese-pupiform, squat cylindrical spire with low domed-shaped apex with protoconch barely elevated above following whorl. Shell wall opaque.  Ground color light tan with obsolescent mottling with lighter irregular spots and streaks that do not form distinct pattern. White streaks most conspicu­ous on ribs. Peristome and adjacent interior of aperture white. Deeper within aperture, inner wall and axis very light rust-colored. Shell 10.5-12.3 mm long, 4.2-4.8 mm wide, and 0.35-0.41 times as wide as long. Shell contains 8.2-9.1 whorls separated by weakly impressed suture. Protoconch with two smooth whorls. Following whorls sculptured with numerous, relatively strong, oblique thread-riblets nearly equally developed on apex and ear­lier whorls of cylinder, becoming obsolete on lower two whorls. Upper ends of riblets do not crenulate suture. Umbilicus imperforate or narrowly rimate. Perisrome relatively thin, weakly reflected, and discontinuous across parietal wall, where it is replaced by thin callus. Ovate aperture slightly higher than wide, 0.26-0.32 times shell length, and 0.63-0.72 times shell width. Aper­ture slightly prosocline in lateral profile, not noticeably thickened within, Axis enlarged in apical whorls (Figure 10).  In cylindric part of shell axis nearly straight, narrower, becoming narrowly perforate or solid by last whorl. (Measurements based on the holotype and ten paratypes are given in Table 2.)

Anatomy: Unknown.

Type Locality: A limestone ravine 15.8 km by road southwest of Pinal de Amoles, Querétaro State, Mexico (21.15°N, 99.65°W), 2585 m alt.

Type Material: Holotype UF 34298; collected 27 September, 1970 by Fred G. Thompson; Paratypes UF 435015 (25), CN MO 3373(5); all from type locality.

Distribution: Querétaro State,  known from the type locality and a nearby locality 2 km ENE of Pinal de Amoles, 2140 m alt. (UF 268262).

Remarks: For meristic comparisons with other spe­cies see Mexistrophia inexpectata new species, below.

Etymology: The species name obsoleta (Latin) refers to the barely discernable reticulated color pattern on the shell, and its sculpture, which becomes obsolete on the last two whorls.

Table 2. Mexistrophia obsoleta new species. Measurements in mm of the holotype (UF 34298) and 10 paralypes (UF 435015) selected to show variation,SL =standard length, SW = standard width, ApH = aperture height, ApW =aperture width, Wh = whorls.

                         SL       SW      ApH    ApW       Wh      SW/SL   ApH/SL   ApW/SW

Holotype         11.2      4.2       3.4       3.1       8.3       0.38        0.29        0.81

Para types

min                  10.5     4.2       3.2       2.7       8.2       0.35        0.26        0.63

max                 12.3     4.8       3.5       3.4       9.1       0.41        0.32        0.71

avg                  11.38   4.36     3.33     2.59     8.52     0.38        0.29        0.68

STD                 0.56     0.20     0.11     0.18     0.30     0.02        0.02         0.05"

(Thompson, 2011:186)

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