82 STEGOCEPHALI CHAP. 



Chelydosaurus from the Lower Red Sandstone of Bohemia was 

 3 feet long, and possessed a beautiful, complicated, ventral armour, 

 consisting of about sixty chevron-shaped rows, about three times 

 as numerous as the vertebrae in the corresponding region. 

 Sphenosaurus from the same strata and localities must have been 

 2 yards long. The trunk-vertebrae of both these genera were 

 composed of four pairs of arcualia. Trimerorhachis from the 

 Permian of Texas is very imperfectly known, but its trunk- 

 vertebrae, as the name implies, consist of three pairs of separate 

 arcualia, one of which, the interdorsal pair, tends to form a kind 

 of centrum. 



Dissorophus multicinctus, also from the Permian of Texas, has 

 been described by Cope * as a " Batrachian Armadillo," and con- 

 sidered allied to Trimerorhachis. Ten vertebrae are known, of 

 an aggregate length of 93 mm. ; the length of the creature was 

 perhaps one yard. The neural spines are elevated, and the apex 

 of each extends in an arch on each side to the ribs. These 

 spinous branches touch each other, forming a carapace. Above, 

 and corresponding to each of them, is a similar dermal and 

 osseous element, which extends from side to side without inter- 

 ruption in the median line, forming a dermal layer of transverse 

 bands which correspond to the skeletal carapace beneath it. This 

 creature remotely approaches the genus Zatachys, Cope, where a 

 dermosteous scute is co-ossified with the apex of the neural 

 spine. The systematic position of this genus is at least 

 doubtful. 



Arcliegosaurus decheni from the Lower Eed of Germany, 

 known by many well-preserved specimens, reached a length of 4 

 or 5 feet. The trunk vertebrae are tri-partite, those of the tail 

 quadri-partite, like those of the trunk of Chelydosaurus. Young 

 specimens show traces of gill-arches. The thoroughly terrestrial 

 walking limbs have four fingers and four toes ; the arrangement 

 of the tarsalia, most of which are ossified, lend support to the 

 view that the morphological axis went through femur, fibula, 

 intermedium, the centralia, the second distal tarsale, and the 

 second toe. The dentine and enamel of the teeth are much 

 folded, and this feature, which applies to most members of this 

 Order, to a lesser degree also to others, has caused them to be 

 comprised under the name of LABYRINTHODONTA. The upper 



1 Amer. Natural, xxix. 1895, p. 998. 



