218 



THE EXTINCT BATRACHIA, KEPTILIA 



The form of the centrum presents one marked peculiarity. The superior rim of the 

 cup is excavated for the passage of the spinal cord, and the hall is concave on its superior 

 aspect, appropriately to the same. This is marked on cervicals and dorsals, and faintly 

 indicated on proximal caudals. There are no ridges on the centrum. There is a gradual 

 increase in length from the cervicals to the dorsals and lumbars. Those in the proximal 

 caudals are much like the same in Mosasaurus, that is, rounded below, and with three su- 

 perior faces, the lateral being the longest. The distal caudals are much compressed. 



The neural spines of the cervical vertebra; commence about opposite the notches between 

 the zygosphens and zygapophyses, and are attenuated anteriorly; they are stouter behind. 

 The ninth, (the first preserved), and probably those anterior, have an acute edge behind 

 as well as before. No neural spine is perfect among the dorsals, but on the fifteenth the 

 position is preserved .75 the length of the centrum; the thinness of the; broken edge 

 would indicate that there had not been as much lost. The posterior edge is nearly oppo- 

 site to the ends of the zygapophyses ; its posterior slope is considerable. , They are evi- 

 dently shorter than in Mosasaurus. 



The neural spines of the caudals are various. The more anterior are thicker behind 

 and alate in front, narrowing to the tip. The median are of similar form, but equally 

 alate anteriorly and posteriorly, 'flu; more posterior are much narrowed at the base, and 

 present only the ahe towards the extremity; the last are not wider than the haemal 

 spines. 



The chevron bones have been at an earlier age separated from the centra, but as in 

 Platecarpus, they are entirely coalescent with their bases. In Mosasaurus the separation 

 persists. They have two short haemapophysial limbs, and a, very long tapering spine, 

 which is grooved in front. On a middle caudal, it is much longer than the centrum and 

 neural spine, and as long as 4.5 centra adjacent. All the haemal arches arc; directed ob- 

 liquely posteriorly. No vertebra without them have been preserved. 



Hypapophyses exist on the ten cervical vertebra?. As in Mosasaurus, their extremi- 

 ties are concave, and are articulated to distinct bones which represent a distinct hypapo- 

 physial ossification. These bones may be compared to short, compressed unguea] pha- 

 langes. The articular extremity of the first is nearly plane, of the others conic, with an- 

 teroposterior enlargement. They are directed posteriorly, and have a broad obliquely 

 ovate outline on the lateral view. Their extremities are rugose. 



The rib.H commence at the axis, which has borne a small oik;. There is no distinct 

 parapophysis, hence each rib-head is undivided, but is flattened vertically. The anterior 

 may he known by the greater compression of both head and shaft. The rib of the third 

 vertebra, has a narrow, convex, articular surface, and is concave on the anterior face. That 

 of the fifth is much wider, and with more truncate head. That of the sixth was found 



