. Bulletin of the British Museum (Natural History). 162 CLEAL & SHUTE. Fig. 9 Neuropteris heterophylla. Cuticle from adaxial surface of pinnule showing differentiation of cells in costal and intercostal fields, photographed using bright field illumination. $l, x 125. lower half of the pinnule, but in the largest forms it may extend for up to two-thirds of the pinnule length. This decurrcnt midvein is never very pronounced, being only slightly wider than the lateral veins. Lateral veins occur alternately on either side of the mid- vein, attached at intervals of 0-5-1-0 mm. T
. Bulletin of the British Museum (Natural History). 162 CLEAL & SHUTE. Fig. 9 Neuropteris heterophylla. Cuticle from adaxial surface of pinnule showing differentiation of cells in costal and intercostal fields, photographed using bright field illumination. $l, x 125. lower half of the pinnule, but in the largest forms it may extend for up to two-thirds of the pinnule length. This decurrcnt midvein is never very pronounced, being only slightly wider than the lateral veins. Lateral veins occur alternately on either side of the mid- vein, attached at intervals of 0-5-1-0 mm. They initially lie at a low angle to the midvein, extend for a short distance in an approximately straight line, and then arch to meet the pinnule margin at 80°-90°. They may branch up to four times, depending on the width of the pinnule. The angle of branch- ing is usually 20°-30°, which often gives the veining a some- what fiexuous appearance. The vein density along the pinnule margin may vary from 40 to 55 per cm, but is usually between 48 and 52 per cm. Cuticles The adaxial cuticles from the pinnules appear robust, but have weakly developed intercellular flanges (Fig. 9). There is some differentiation in cell structure in the costal and inter- costal fields. In the costal fields, the cells are elongate and subrhomboidal, up to 150 |im long x 20 |im wide (Fig. 17). Their long axes are aligned approximately parallel to the veins. In the intercostal fields the intercellular flanges are very weak, but there is a faint impression of shorter and more irregularly polygonal cells, up to 50 |im long x 20 \im wide (Fig. 18). Again, their long axes are aligned more or less parallel to the veins. The abaxial cuticles are significantly thinner, and only small fragments could be prepared. Intercellular flanges, although not prominently developed, arc clearly visible. Costal cells arc elongate, parallel-sided and approximately 15 |im wide. It was impossible to determine their length. T
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