334 Mr. C. W. Andrews on the Development of 



mentioned, and maybe provisionally referred to thegenus Cryp- 

 toclidus^, a division established by Professor Seeley f for the 

 reception of forms which are distinguished from Murceno- 

 saurus by possessing vertebras with broader, shorter, and more 

 concave centra, less cylindroid zygapophyses, and, in the 

 cervical region, shorter neural s])ines ; coracoids with large 

 postero-lateral. prolongations ; clavicles which meet in the 

 middle line, the interclavicle being absent ; radius of great 

 vertical depth and ulna transversely elongated. It is not 

 clear whether Professor Seeley himself considers CryptocUdus 

 a distinct genus or merely a subgenus of Murcenosaurus, 

 since he speaks of it in both ways ; but there can be no doubt 

 that it is entitled to generic rank, since in the number and 

 form of the cervical vertebrae the animals referred to it are 

 totally different from the Murasnosaurs ; moreover, in the rest 

 of the skeleton, e. g. the pectoral arch, constant differences 

 can be detected. 



The following diagnosis of the genus may be given, the 

 characters being determined from the type of C. platymerus 

 and other specimens in the Leeds collection : — Skull about 

 one third of the length of the neck, with broad blunt snout. 

 Mandible with very short symphysis. Cervical vertebree 

 31-32 in number; centra short and with rather deeply con- 

 cave oval articular surfaces, the width of which is considerably 

 (as 7 to 5) greater than the length of the centrum ; zyga- 

 pophyses cylindroid, zygosphenal articulation well developed. 

 There are 2 or 3 pectoral vertebrse and 21 or 22 dorsal, all 

 with concave articular ends. There appear to be 3 or 4 sacral 

 vertebra, distinguished by bearing ribs, which are expanded 

 at the outer ends and articulate partly on the centrum and 

 partly on the neural arch. The abdominal ribs are very 

 strongly developed and are arranged in about ten transverse 

 rows, each consisting of a median piece and two lateral pairs. 

 The chevrons, at least in the adult, impress the vertebree both 

 in front and behind them. In the adult the ventral rami of the 

 scapulas meet in median symphysis and extend back to meet 

 the median anterior prolongation of the coracoids, closing the 

 coraco-scapular foramina ; anteriorly they extend beneath 

 the clavicles. These latter are triangular membrane-bones 

 which meet in median symphysis ; there is no known inter- 

 clavicle. The coracoids are very thick and massive in front, 



* It is not improbable that this genus is identical with Colymhosauriis, 

 established by Professor Seeley in 1874 on the evidence of a shoulder- 

 girdle from Ely. If this shoid'd prove to be the case, the name Culymbo- 

 saurvs, having the priority, must be adopted for these Plesiosaurs. 



t Proc. Roy. Soc. vol. li. (1892) p. 145. 



