EDENTATA OF THE SANTA CRUZ BEDS. 32 1 



In Santa Cruz times the members of this family were far less abundant 

 and varied than the Megalonychidce, which they much exceed in average 

 size ; the largest known Gravigrada from the formation belong to the 

 Planopsida and none of them are very small. The teeth are non-lobate 

 and the small upper caniniforms, which in all known examples are isolated 

 by diastemata, are inserted far behind the anterior border of the maxillary. 



The skull is elongate and cylindrical, with no trace of a sagittal crest, 

 but with the cranial roof more or less flattened and having some cancelli 

 and incipient sinuses in the parietals. The premaxillae are not known, 

 but the facets for them upon the maxillaries show that they must have been 

 quite different from those of the preceding family, and the rostrum is longer; 

 the palate is much less convex and rugose. 



In no genus of the present family is the number of trunk-vertebrae 

 known, but there is good reason to believe that the back was very long 

 and that the number of vertebrae was quite equal to that which is found in 

 the contemporary Megalonychidce. A difference from the latter family is 

 to be observed in the lumbar region, where a second pair of accessory pre- 

 and postzygapophyses is added. The tail is extremely heavy. 



The bones of the fore-limb have a general resemblance to those of the 

 preceding family, but are considerably longer in proportion ; those of the 

 manus show many differences of detail, the most important of which is the 

 shape of the ungual phalanges, which are much broader, more decurved 

 and blunter than in the Megalonychida. 



The pelvis is chiefly remarkable for the great elongation of the pubes 

 and ischia, which produces a decided resemblance to Megatherium. The 

 femur is extremely broad and antero-posteriorly compressed and flattened, 

 much more so than in the preceding family, while the tibia differs less 

 from that of the latter. Little is known of the pes, but the calcaneum and 

 astragalus have certain very significant characteristics. As compared with 

 those of the Megalonychidce, the following differences may be noted : (i) 

 the astragalus has entirely different proportions, being much shorter and 

 broader ; (2) the inner condyle is much shorter proximo-distally, strongly 

 convex and projecting prominently towards the inner side ; this is obvi- 

 ously the first stage in the remarkable transformation of the astragalus 

 which characterizes Megatherium; (3) the calcaneum has a much more 

 prominent sustentaculum, the astragalar surface of which presents dorsally 

 instead of distally, and the cuboid facet is very narrow dorso-ventrally. 



