48


Journal of Paleontology 90(1):43–58


Figure 4. Lectotype of Douvilleiceras spiniferum (Whiteaves, 1876), GSC No. 5014b, Skidegate Inlet, west of Alliford Bay, exact locality not recorded (Coll. J. Richardson, 1872). (1) ventral, and (2) left lateral views of plaster cast of lectotype, coated with ammonium chloride.


irregular in strength. The first ventrolateral tubercle appears at about 6.2mm in diameter as a faint conical elevation on the ventrolateral part of the ribs. At the same stage, the lateral tubercles are represented by a long spine. With further growth, the ventrolateral elevation becomes gradually higher, and then forms a distinct tubercle at approximately 7.5mm in diameter, although it is not yet clavate. At approximately 11.5mm in diameter, the third row of tubercles appears ventrolaterally to the second row of tubercles, and the ribs between the first ventrolateral tubercles have disappeared or become quite faint. In this stage, the first ventrolateral tubercles appear to be clavate. The first umbilical tubercles, forming the fourth row, develop along the umbilical margin at approximately 14.5mm in diameter. At 22mm in diameter, the third ventrolateral tubercle forms ventrolaterally to the second ventral tubercle (Fig. 6.1). Finally, at approximately 43mm in diameter, a faint spinose tubercle appears between the lateral tubercle and the umbilical one. Regarding such ontogenetic changes as appearance or disappearance of tubercles and ribs, the present species shows great variation between individuals (Fig. 5.2, 5.3). The sutural elements of D. spiniferum at middle growth


stage are of typical Douvilleiceras form, characterized by fairly deep and narrow external and lateral lobes, and a broad


and somewhat rounded first lateral saddle (E/A) (Fig. 7.2). The suture line of the extremely early growth stage is, unfortunately, not observed. At D ≈ 1–2mm, however, the suture is expressed as EAUI, while atD >2.5mmit is expressed as EAU2U1I, as shown in Figure 7.1. The suture of the later growth stage is given as EAU2U1I (Korn et al., 2003). The pattern of ontogenetic change of the suture line of D. spiniferum is closely similar to that of D. “charshangense” figured by Mirzoyev (1967, p. 56, fig. 2).


Occurrence.—This species is common in the lower part of the Haida Formation, particularly in the Brewericeras hulenense Zone (= mammillatum Zone) on Maude Island, and particularly in the Leymeriella (L.) tardefurcata and D. mammillatum zones, the lower Albian of the Lower Greensand of southern England.


Material.—A large number of additional GSC specimens were obtained from calcareous concretions collected at GSC Loc. C-300855, whereas a few other specimens were collected from GSC localities 7591a, C-304101, C-304102, and GSC C-304103. All of these latter four localities are in the lower part of the Haida Formation.


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