in the Museum of Buenos Ayres. 9S 



iliac bone ; those of the back part are placed longitudinally, and 

 parallel to the median crest of the os sacrum, belonging to the 

 ischial bone of the pelvis, and rising towards the place to which 

 are joined the lateral prolongations of the last sacral vertebra. 

 The two posterior alae are distant from each other, but the 

 anterior ones unite in the centre of the animal, and, with the 

 high crest of the first three vertebrae of the os sacrum, form 

 a cross below the centre of the posterior and heaviest part of 

 the shell. The iliac bone descending from this spot inclines 

 a little inferiorly, forming at its lower end the articulation for 

 the thigh termed the acetabulum, into which enters the hemi- 

 spherical head of the femur. The direction of that part of the 

 principal postirior ramus of the pelvis, termed the ischium, runs 

 almost horizontally towards the place of the posterior ascending 

 ala, which is a subcylindrical and very thick bone, extending 

 inferiorly into a long perpendicular and slightly inclined plate. 

 The OS pubis, on the contrary, is very slender, similar to a small 

 rod, which extends a little at the lower end, unites with the 

 ischium, and forms a symphysis pubis, which until now was not 

 known in the Gli/ptodon, as it is absent in all the pelves dis- 

 covered. For this reason, we must calculate that it was very 

 slender and delicate, being perhaps a little open in the centre, 

 and merely united by cartilaginous substance, which is also the 

 esse with the Peludos and with the Mataeos of the present 

 day. 



We perceive behind the pelvis the vertebral column of the 

 tail, w^hich is rather strong and composed of loose vertebre of 

 different number in different species. Each vertebra possesses 

 a thick cylindrical part below, and a vertebral arch above, from 

 which issue three perpendicular prolongations anteriorly and one 

 horizontal one, with two obtuse points posteriorly. Of these 

 the centra] one is the spinous process, and the other four the 

 oblique processes. There issues from each side of the body of 

 the vertebra, and between these processes, a transverse process 

 with an elevation at its extremity. All these parts gradually 

 diminish in a posterior direction, the last vertebra being a conical 

 body w^ithout any arch or process on its surface. Generally the 

 three vertebra; at the base of the tail are not only the largest, 

 but also differ by their more extended transverse processes ; in 

 the following ones this process is shorter, and at the end more 

 reclinate, because it is these vertebne which are connected with 

 the caudal rings, and the three basal ones are not. 



I am only able to state with exactitude the number of the cau- 

 dal vertebrae of G. spinicaudus ; they are ten, of which six are 

 met with in the caudal rings. According to the specimens ex- 

 hibited in the Museum, we can calculate with exactitude that 



