THOMPSON: Humboldtiana from Chihuahua and Texas
87
Humboldtiana princeps n. sp.
Diagnosis. The helicoid or depressed-helicoid shell is large, up to 41 mm wide. It is light brown with three chestnut-brown bands and transverse white streaks, and it has a slight luster. The transverse whit? streaks are less numerous than in other species of Clydonacme, and they tend to be broken more frequently. The embryonic whorls bear relatively coarse transverse zigzag threads that are beaded. The postembryonic whorls are sculpture with relatively fine incremental striations and weak growth wrinkles. The first postembryonic whorl bears numerous fine microscopic granules throughout the length of the whorl. The genital atrium is moderately long and slender. The penis is club-shaped with a slight apical constriction; internally it bears a large verge that is half the length of the cavity, and the inner wall is lined with 5-6 heavy fleshy folds. The epiphallus is slightly longer than the penis, and the relatively slender flagellum is slightly longer than the combined length of the penis + epiphallus. The vagina bears four dart-sacs; ds, is the largest, and the other three are greatly reduced in size. The dart-glands form a ring around the vagina a short distance above the dart-sacs. The spermatheca + duct bears a caecum and is very long, being about twice the length of the uterus.
Shell (Fig. 54-59). The shell is up to 41 mm wide, and is helicoid to depressed-helicoid in shape; 0.83-1.02 times as high as wide. There are 4.0-4.2 whorls that are inflated and have a moderately impressed suture. The whorls regularly expand until the last quarter whorl, which rapidly descends to the aperture (Fig. 55). The upper lip of the peristome inserts on or just below the sub-peripheral band. The periostracum is nearly smooth and has a low luster. The umbilicus is narrowly, obliquely rimate (Fig. 57). The ground color is light brown with three chestnut-brown bands. The bands are unequal in width. A lighter chestnut zone usually borders the suture along the upper side of the whorls. Frequent transverse white streaks, which lie on the growth wrinkles, interrupt the underlying color patterns. The interior of the aperture is light grayish-brown and banded. The peristome is light brown, and the parietal callus is hyaline. The 1.5 embryonic whorls are raised. The first embryonic whorl is 3.9-4.1 mm wide transverse to the initial suture. The embryonic sculpture consists of relatively coarse zigzag transverse threads that are beaded by granules. The postembryonic whorls have relatively fine incremental striations and low growth wrinkle. In addition, the first postembryonic whorl has numerous granules that tend to be aligned along the growth wrinkles. The granules occur throughout the
length of the whorl, but are densest along the lower 3A of that whorl. Granular sculpture is absent on the lower whorls. The aperture is broadly obovate in shape; 0.76-0.84 times as wide as high. The plane of the aperture lies at an angle of 40-42 to the shell axis. The peristome is weakly but uniformly reflected along the upper and outer lips; more so along the basal lip, and strongly so over the columellar area.
Measurements of the holotype and twelve paratypes are given in Table 8.
Anatomy (Figs. 60-62). Three specimens were dissected (UF 21331). The genital atrium is 2-3 mm long and slender. The penis is 12-15 mm long and tapered. It is widest below the epiphallus. The upper end of the penis has a slight constriction, which corresponds to the absence of internal folds at that point. The inner wall of the penis has 5-6 longitudinal folds that extend from below the apical constriction to the base. The penis contains a large verge in the upper third of chamber (Fig. 61). The penis retractor muscle is 14-17 mm long and is slightly longer than the penis. The penis retractor muscle originates on the middle of the inner wall of lung about 3-4 mm behind the mantle collar, and inserts on the end of the penis laterad to the epiphallus and forms a narrow sheath around the lower end of the epiphallus. The epiphallus is 15-18 mm long, stout, thick-walled, and is slightly longer than the penis. It is lined internally with four longitudinal folds. The flagellum is 33-42 mm long, relatively slender and is slightly longer than the combined length of the penis + epiphallus. It is lined internally with four longitudinal folds. The vas deferens is moderately stout below the prostate and above the epiphallus, and is very narrow in its middle where it is attached by connective tissue to the genital atrium. The lower vagina is relatively long and is conical and it bears four unequal sized dart-sacs. One dart-sac, ds,, is large and bulbous; the other three dart-sacs are much smaller and are about equal in size to each other. The dart-glands encircles the middle vagina a few mm above the dart-sacs. The spermathecal duct diverges from the free vagina 1 -2 mm above the dart-glands. It is moderately stout and very long. The spermatheca + duct is 97-113 mm long. The duct bears a short caecum at 0.69-0.76 of the distance from the base. The caecum is about half or less than the length of the remaining spermatheca + duct. The spermatheca is small, elongate-bulbous, and is oppressed against the upper end of the uterus-prostate at the base of the albumen gland. The spermatheca + duct is about twice the length of the uterus. The uterus is 47-52 mm long.
Type locality. Chihuahua, 13 km southwest of Cd. Chihuahua (2837'N, 106 10'W); 1540 m alt. Holo-