. Bulletin of the British Museum (Natural History) Geology Supplement. 66 ELOPIFORM FISHES soc exo ot. s c. par Fig. 31. Megalops cyprinoides (Broussonet). Neurocranium in posterior view. Based on same specimen as Text-fig. 30. The neurocranium of Megalops is relatively deeper and the maximum depth occurs at the sphenotic level, whereas in Tarpon the maximum depth is at the occiput. The depth of the Megalops neurocranium is due to the depth of the prootic bone and parasphenoid ascending wings which in turn may be related to the invasion of the skull by the swimbladder in the following manner.


. Bulletin of the British Museum (Natural History) Geology Supplement. 66 ELOPIFORM FISHES soc exo ot. s c. par Fig. 31. Megalops cyprinoides (Broussonet). Neurocranium in posterior view. Based on same specimen as Text-fig. 30. The neurocranium of Megalops is relatively deeper and the maximum depth occurs at the sphenotic level, whereas in Tarpon the maximum depth is at the occiput. The depth of the Megalops neurocranium is due to the depth of the prootic bone and parasphenoid ascending wings which in turn may be related to the invasion of the skull by the swimbladder in the following manner. Megalops has a large eye, relatively larger than that in Tarpon, and thus might be expected to have a large posterior myodome. The extreme anterior end of the swimbladder diverticulum is received in a deep pit within the prootic bone immediately above the prootic bridge, which is, in consequence, displaced ventrally. This lowering of the myodome roof would restrict its volume. Hence it is suggested that the myodome volume is maintained by effectively lowering its floor, by deepening the prootic and para- sphenoid walls. Correlated with this deepening is the angled parasphenoid which is in contrast to the relatively straight bone seen in Tarpon. The intercalar bone of Megalops has been well described by Greenwood (1970a), who recognized three interconnected portions ; a basal portion, a lateral shield-like part and a saddle-like wing. The lateral shield-like portion forms a complete bony outer wall to the periotic bulla and is joined to the prootic, basioccipital and exoc- cipital by a syndesmotic union. The anterior swimbladder diverticulum occupies. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)


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