136 Prof. H. G. Seeley. The Shoulder Girdle 



centrum, as are the caudal ribs. To these characters may be added 

 from Professor Cope's figures ; neural arch depressed, with massive 

 neurapophyses, and small neural canal. These characters help to 

 define the genus from Uronautes. Phalanges remarkably short. The 

 author subsequently states (' Amer. Naturalist,' 1887, p. 564) that in 

 Polycotylus the neurapophyses and all diapophyses and parapophyses 

 are co- ossified with the centra. 



In Piptomerus (' Amer. Naturalist,' 1887) the neurapophyses and all 

 other processes of the vertebras articulate freely with the centra. 

 The cervical vertebras are short, twice as wide as long, and deeper 

 than long. The dorsal vertebrae are two-thirds as long as the cervi- 

 cals, deeper, and rather narrower. 



In Orophosaurus the neural arches are co-ossified, and the par- 

 apophyses free. The centrum is a little wider than deep. 



In Uronautes both neural arches and parapophyses are co-ossified. 

 All vertebrae are short, nearly twice as wide as long, as deep as wide, 

 centrum biconcave, neurapophyses lamellar, neural canal large. 



In the American specimens referred to Plesiosaurus Professor Cope 

 states that the neural arches of the vertebrae are loosely articulated. 



Until the American types are fully figured it will not be possible to 

 judge whether these genera are all founded on characters which will 

 enable them to be recognised in adult individuals. 



In Elasmosaurus the characters given for the genus are : Neural 

 arch anchylosed with the centrum ; cervical centrum longer than deep, 

 deeper than wide ; ribs articulated to oval pits. Vertebrae numerous. 

 The dorsal vertebrae have strong transverse processes. In the caudal 

 vertebrae the articular chevron facets are said to be on the inferior 

 face, near its posterior articular aspect. This condition is not un- 

 known in early caudal vertebrae in English Sauropterygians from the 

 Pelolithic strata, but no evidence has been given that it extends 

 throughout the caudal series in any Sauropterygian species. The 

 scapular arch has the well-known form, with the scapulae meeting in 

 the median line, and continuous posteriorly with the coracoids, so as 

 to enclose two large foramina between the bones. The scapulo-pre- 

 coracoid appears to form about two- thirds of the wall of the glenoid 

 cavity. No clavicle was found. The ilium appears to articulate with 

 the pubis only. No limb bone was found, nor any abdominal ribs. 



Professor Cope states that this genus is distinguished from Cimolio- 

 saurus by the shortness of the neck in the latter, and its elongation 

 in JSlasmosaurus. In Elasmosaurus the cervical centrum is transversely 

 compressed, and comparatively long; while in Cimoliosaurus it is 

 short, broad, and vertically depressed. 



Finally, Mr. P. W. Cragin has described Trinacromerum ('Amer. 

 Geol.,' vol. 2, p. 405, 1888, and vol. 7, September, 1891, p. 171) from 

 the Cretaceous rocks of Kansas, but no figures of it have yet been 



