142 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



The pattern of ornamentation is, over most of the carapace, essentially 

 the same as in Propalceohoplop horns, but nearly all of the plates are 

 rougher and more coarsely punctate than in the latter. The character- 

 istic feature of Cochlops, which differentiates it clearly from all the other 

 Santa Cruz glyptodonts, is a broad belt of scutes on each side of the 

 carapace, beginning at the eleventh or twelfth transverse row and extend- 

 ing almost to the posterior border. This belt which is rather nearer to 

 the median dorsal line than to the lateral border, is of somewhat irregular 

 width, but generally includes five or six plates of each transverse row. 

 Over most of the surface of the belt the only modification of the sculp- 

 tural pattern consists in the presence of a very small, sharply pointed and 

 conical tubercle, which is placed somewhat behind the middle of the large 

 central figure of each plate. In the pelvic region, however, the pattern is 

 greatly modified; the surface of the plates becomes very rough and in 

 many of them has a wrinkled appearance, the ornamental pattern being 

 nearly or quite obliterated, while in others the central figure is raised into 

 a high, prominent and rugose cone, while the peripheral figures form a 

 ring of lower conical tubercles around it. In each pelvic area there are 

 two groups of plates with these conical elevations, but there is much indi- 

 vidual variation in the development of the cones and in the number of 

 plates upon which they are prominent. Always, however, there is one 

 plate in the posterior group which most clearly and strongly displays 

 these features. In this region of modified ornamentation two or more 

 plates of the same transverse row may be coossified. 



Lydekker has suggested ('94, 49) that these modified plates belong to 

 aged individuals of Propalceohoplophorus, of which he regards Cochlops as 

 a synonym. The much more abundant material contained in the recently 

 made collections does not at all confirm this suggestion, but strengthens 

 the opinion that the genera are distinct. 



The tail-sheath (Plate XIX, fig. 2) resembles that of the preceding 

 genus, but has certain characteristic modifications ; it is made up of five 

 anterior quite freely movable rings, and a posterior stiff, club-like mass, 

 likewise composed of four rings of two rows of plates each ; this portion 

 is more tapering and less abruptly truncated than in the preceding genus, 

 and its plates are thinner. The ornamentation of the anterior rings is 

 nearly the same in the two genera, but in Cochlops the median ridge of 

 the central figure ends in a somewhat more prominent posterior point. 



