. Bulletin of the British Museum (Natural History). 268 D. S. BROWN. Fig. 10 Cryptodidus eurymerus (Phillips). Composite skeletal reconstruction with animal engaged m subaqueous flight locomotion. Overall length of adult about four metres. See 'Note on the reconstruction", p. 280. There are three specimens of C eurymerus in which 55 presacral vertebrae are preserved. In , which is a 'juvenile', there are 32 cervicals, 3 pectorals and 20 dorsals, and this is also the estimated distribution of vertebral types in the 'adult' specimen In the 'old adult' the estimate of 29
. Bulletin of the British Museum (Natural History). 268 D. S. BROWN. Fig. 10 Cryptodidus eurymerus (Phillips). Composite skeletal reconstruction with animal engaged m subaqueous flight locomotion. Overall length of adult about four metres. See 'Note on the reconstruction", p. 280. There are three specimens of C eurymerus in which 55 presacral vertebrae are preserved. In , which is a 'juvenile', there are 32 cervicals, 3 pectorals and 20 dorsals, and this is also the estimated distribution of vertebral types in the 'adult' specimen In the 'old adult' the estimate of 29 cervicals, 3 pectorals and 23 dorsals suggests that the position of the transition from cervicals to dorsals is subject to variation. If a constant number of presacral vertebrae in this species is assumed from the evidence of 3 specimens with the maximum recorded number, then it must also be assumed that specimens with rather less than 55 presacrals (such as with 53, with 48) have been incompletely collected. Since the bones are disarticulated and entirely clear of the matrix, this cannot be checked but seems probable. The vertebral column of plesiosaurs shows several features which do not vary significantly throughout the suborder but have sometimes been used erroneously for taxonomic purposes. These include relative size of vertebral types; proportional length of neural spines; relative diameter of the neural canal; relative development of zygapophyses and presence of nutritive foramina. In these features the present species is typical of all forms. In any individual the largest vertebrae are the mid-dorsals, and these have proportionally (as well as actually) the longest neural spines. The diameter of the neural canal is maximal in the posterior dorsal vertebrae, and reduces both posteriorly and anteriorly. The zygapophyses of dorsal and caudal vertebrae are small and weak, whereas those of cervical vertebrae are large and well developed. Williston (1914) thou
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