Dactylioceras ( Orthodactylites ) cf. tenuicostatum ( Young and Bird, 1822 )

Dactylioceras ( Orthodactylites) cf. tenuicostatum ( Young and Bird, 1822)

Fig. 4N, R.

Material.—Four fragmentary and crushed specimens from Kuhe Bashm (050510−13/1, 050513/2, and from earlier collections by K.S.−E. (80−SE−5, 80−SE−19).

Discussion.—The wide umbilicus with extremely fine and dense ribs allows the fragmentary specimens to be compared with D. ( O.) tenuicostatum and allied forms, discussed and figured by Howarth (1973: 258, pl. 5: 1, 2; pl. 6: 2, 3) and Howarth (1980: 650, pl. 82: 1–10, 13, 14).

Stratigraphic and geographic range.— Kuhe Bashm, level III. D. ( O.) tenuicostatum has been recorded from the Lower Toarcian Dactylioceras tenuicostatum Zone.

Dactylioceratidae indet.

Fig. 4O.

Material.—One fragmentary phragmocone collected by Hosseinzadeh (2003) from Kuhe Bashm (H−204).

Description.—At a diameter of 20 mm the specimen is relatively evolute with an ovate whorl cross−section and flanks converging slightly towards the arched venter. The last preserved whorl becomes distinctly involute with a deep umbilicus and a vertical umbilical wall. Moreover, the whorls become considerably wider (W/H ratio = 92%), with flanks converging strongly towards the venter, resulting in a triangular−ovate whorl cross−section. The ribbing is extremely fine, dense, and sharp. The slightly prorsiradiate primaries (22 per half−whorl at D = 20 mm) bifurcate almost regularly about the mid−flank. The slightly finer secondaries cross the arched venter in a straight line. No tubercles are developed at the bifurcation point. Discussion.—To some extent, the specimen has the appearance of a Macrocephalites . The narrow umbilicus and the fine ribbing of the last preserved whorl resembles Dactylioceras ( Iranodactylites) ketevanae Repin (2000: 40 , pl. 3: 1, 2), from which our specimen differs by its distinct broadness and a nearly triangular whorl cross−section. A very similar, perhaps conspecific specimen is Dactylioceras sp. nov. from the Shemshak Group of the Lut Block, East Central Iran ( Seyed−Emami et al. 2004: 81, pl. 1: 3a, b). However, the latter has a finer and denser ribbing.

Stratigraphic and geographic range.— Repin (2000: 41) recorded D. ( I.) ketevanae from the Hildoceras bifrons Zone. The specimen from the Lut Block comes from the Lower Toarcian ( Seyed−Emami et al. 2004). Hosseinzadeh (2003: 67) found the described specimen, together with D. ( O.) semicelatum , in the Dactylioceras tenuicostatum Zone of the Early Toarcian.