. A descriptive catalogue of the marine reptiles of the Oxford clay. Based on the Leeds Collection in the British Museum (Natural History), London ... Reptiles, Fossil. 170 MARINE EEPTILES OF THE OXFOED CLAY. Chevrons (text-fig. 6S).—Of the chevrons no good series is available for description. The anterior chevrons (text-fig. 08, A) are of the ordinary Y-shape, the arms being rather shorter than the ventral process; above they terminate in an oblique rounded facet for union with the facets on the hinder ends of the centra of the caudal vertebras. At the junction of the two arms the bone is com
. A descriptive catalogue of the marine reptiles of the Oxford clay. Based on the Leeds Collection in the British Museum (Natural History), London ... Reptiles, Fossil. 170 MARINE EEPTILES OF THE OXFOED CLAY. Chevrons (text-fig. 6S).—Of the chevrons no good series is available for description. The anterior chevrons (text-fig. 08, A) are of the ordinary Y-shape, the arms being rather shorter than the ventral process; above they terminate in an oblique rounded facet for union with the facets on the hinder ends of the centra of the caudal vertebras. At the junction of the two arms the bone is compressed from before backwards, but at the lower end the compression is lateral. The exact form and arrangement of the other chevrons cannot be made out from any specimen, but, judging from the skeleton of Geosaums (frontispiece), the condition seems to have been as follows:—As the chevrons are followed backwards towards the bend in the tail they become smaller and the upper arras of the upper Y shorten and widen. At the same time they slope considerably backwards, and a forwardly-directed process arises from the angle of the Y, giving them the appearance shown in text-fig. 08, B, C. Behind the bend of the tail the ventral part of the chevron is greatly enlarged, strongly compressed laterally, and Text-fiff. 68,. Chevron-bones of Melriorhynchus superciliosum : A, anterior chevron from front; B, posterior chevron from left side; C, from front; D, chevron from end of tail, from left side, and (E) front; E, posterior chevron from left side. (R. 1530, § nat. size.) , anterior process ; /., facet for union with vertebra. with its ventral border notched in the middle (text-fig. OS, 1), E). The anterior and posterior ends of the expanded portion bear oval facets apparently for union with the chevrons in front and behind, so that in this region the chevrons form a closed series, much like a row of strongly compressed centra; this arrangement must have greatly strengthened this
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectreptile, bookyear1910
