. Bulletin of the British Museum (Natural History). 168 CLEAL & SHUTE 10 cm. Fig. 26 Neuropteris heterophylla. Drawing of specimen shown in Fig. 1, showing dichotomy of primary rachis near the base of the frond. , X Fig. 28e, it is impossible to determine whether they are alternating long and short, as is characteristic of the lower part of the frond. This demonstrates the difficulty of position- ing such small specimens within so complex a structure as the N. heterophylla frond. Size and degree of pinnadon of secondary pinnae. No com- plete secondary pinnae have been
. Bulletin of the British Museum (Natural History). 168 CLEAL & SHUTE 10 cm. Fig. 26 Neuropteris heterophylla. Drawing of specimen shown in Fig. 1, showing dichotomy of primary rachis near the base of the frond. , X Fig. 28e, it is impossible to determine whether they are alternating long and short, as is characteristic of the lower part of the frond. This demonstrates the difficulty of position- ing such small specimens within so complex a structure as the N. heterophylla frond. Size and degree of pinnadon of secondary pinnae. No com- plete secondary pinnae have been found attached to the outward-facing sides of the primary pinnae in the basal part of the frond. The longest known examples are 13 cm long (Fig. 26; see also Laveine, 1967: pi. 11, fig. 1), but are clearly very incomplete. The longest detached example is probably that shown in Crookall (1959: pi. 25, figs 1-2). It is a 17-cm long near terminal fragment of a bipinnate pinna. It is more or less symmetrical about the penultimate rachis, and is thus quite different from the asymmetrical terminals of the primary pinnae (discussed above). In nearly all of the known speci- mens, these outward-facing secondary pinnae are bipinnate. Just one (Laveine, 1967: pis 11-12) shows a tendency to become tripinnate. Size of frond. None of the specimens described in this study, or documented in the literature, are complete enough to give a very reliable estimate of the overall size of the frond. However, using the largest available specimen (Fig. 26) it is possible to assess the approximate distance from the dichotomy to the frond apex (hereafter referred to as the DAD). Assuming that the two primary pinna branches, which curve distally in towards one another, did not overlap significantly at the frond apex, then the DAD in this frond was about 1 m. Using this as a base-line, it is possible to estimate the DAD of fronds in other, less complete speci- mens, using the assumption that frond size is b
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