448 H. GOVIER SEELEY ON EMTS HORDWELLENSIS. 



line ; it is 1| inch broad across the shoulders for the second pair 

 of costal plates, measures nearly 1| inch along the posteriorly 

 converging lateral surfaces for the third pair of costal plates, and 

 is }|- inch wide behind. 



The fourth neural plate is more like the second, but is relatively 

 "wider behind. It is smooth and convex, and measures 1-^- inch 

 in length, is 1^ inch broad over the shoulders for the third pair 

 of costal plates, and measures J-| inch along the posterior sides for the 

 fourth pair of costal plates. These sides do not converge so rapidly 

 as those of the plates in front ; the bone measures -J- inch from side 

 to side behind. 



The fifth neural plate is subquadrate ; it is crossed transversely 

 behind the middle by the scutal impression. It measures 1| inch 

 long, 1| inch broad over the shoulders in front, |-| inch along 

 the lateral border, and if inch wide from side to side behind. 



The sixth neural plate is transversely oblong, | inch long, 1| 

 inch broad, and fully an inch broad behind. 



These neural plates are less than | inch thick ; and to each of them 

 is ankylosed the neural arch of a vertebra. The neural arches are 

 greatly compressed from side to side, and are expanded a little in 

 the middle, where two centrums met and gave attachment to the rib. 

 The neural arches become successively wider from before backward : 

 this character was probably also seen in the centrums. The fifth 

 neural arch has the anterior half of the corresponding centrum pre- 

 served. It is remarkable for compression from above downwards, 

 expansion opposite the rib, and constriction in the middle of the 

 centrum. The rib articulates both with the centrum and with the 

 neural arch. 



The nuchal plate is greatly thickened on the visceral surface, in 

 a line which corresponds to the transverse scutal impression. In 

 front of this line the marginal scutes are prolonged on the under- 

 side of the carapace ; behind it the plate is smoothly excavated as 

 if to form a recess for the animal's head. The first epipleural plates 

 are greatly thickened where they join the marginal plates anteriorly, 

 and have blended with them a pair of strong greatly elevated ribs 

 which curve forward. But the second, third, and fourth epipleural 

 plates show no sign of the confluent rib, except where it rises near 

 the centrum at a sharp angle as a narrow pedicle compressed from 

 above downward. The transverse space between the bases of the 

 first pair of ribs is 1§ inch ; but the distance lessens from before back- 

 ward ; between the fifth pair it has diminished to 1| inch. This 

 pair of epipleural elements has the rib slightly elevated. 



The costal or epipleural plates are all imperfect. The first pair is 

 by far the largest. Each is of irregular form ; and, owing to the fact 

 that it meets the nuchal plate and three marginal plates, its outlines 

 converge towards both ends. It is 2 inches long in a line with 

 the suture between the nuchal plate and the first marginal. 



The second costal plate widens outward from 1J inch near the 

 neural plate to 1| inch where fractured. It is marked with a 

 Y-shaped scutal impression. 



