236 PROF. H. G. SEELEY OX PELOBATOCHELYS BLAKII ETC. 



ary is an impressed line, margined behind by a row of oblong rounded 

 tubercles, which point backward and inward, and are prolonged as 

 faint elevated ridges over the costal and neural plates till they reach 

 the median line of the carapace. The second costal plate is 1J inch 

 long, and is preserved for a width of 2 inches. The rib is completely 

 blended with the epipleural element, both being very thin. The ar- 

 ticular head of the rib is concave, subquadrate, not separated from 

 the costal plate, -f^ inch in diameter, and half an inch distant from 

 the median line of the neural plate. The extreme thickness through 

 the articular head is | inch. 



The third costal plate is about 1| inch long, and is preserved for 

 a width of l|j- inch. On the underside the rib is seen as a thin 

 convex band 1| inch wide. This plate, like the adjacent third neu- 

 ral plate, is crossed just below its middle by the transverse boundary 

 of the second vertebral scute, similarly marked by an impressed line 

 bordered behind by a row of rounded tubercles. The second vertebral 

 scute is therefore 2 J- inches long, and at least as wide as the fragment 

 of the second costal plate. 



Mr. Blake's other specimen is 4| inches long, and displays the 4th, 

 5th, and 6th neural plates. The fourth is half an inch thick, 1| inch 

 long, less than an inch wide in front, and ^ inch wide behind ; it is 

 slightly compressed in the middle. It joins the third costal plate 

 only on the right side, by a narrow band. The costal plate is pre- 

 served on the left side. 



The fifth neural plate is If inch long, more angular than the fourth; 

 its anterior margin is undulating and widens to 1J inch to form 

 shoulders J inch long for the fourth costal plates. It is somewhat 

 constricted in the middle, and widens again at the distal end to J inch. 

 It is crossed at less than an inch from the anterior border by the 

 posterior border of the third vertebral scute. The fifth pair of cos- 

 tal plates are preserved in fragments on both sides, and show the 

 scutal border to have been directed outward and slightly backward. 

 As usual, it is marked by an impressed border in front ; and though 

 still bordered by tubercles behind, these are seen as the terminal 

 teeth of serrations which resemble the teeth of a saw ; and from them 

 elevated ridges are prolonged backward and inward as from the tu- 

 bercles on the anterior part of the carapace. 



The sixth neural plate is about 1 J inch long, J inch wide, with 

 subparallel sides. It is nearly || inch thick, and in section is a de- 

 pressed pentagon. 



The fourth costal plate is 1| inch long and 5| inch wide. The 

 epipleural part extends transversely for 3f inches ; but it is very thin 

 over the rib, and in fact divides as though it were slit, so that the 

 flat striated surface of the rib is exposed for 3| inches. 



At a distance of rather more than 4 inches from the median line 

 of the carapace the faint impression is seen of the middle of the 

 lateral margin of the third vertebral scute, which is about 3| inches 

 long, and is thus shown to have been about 8 inches broad. 



The fifth costal plates are about 1J inch long, and are directed 

 slightly backward like the fourth plate ; but, as preserved, they only 



