GLIRES OF THE SANTA CRUZ BEDS. 



471 



limbs are very much less elongate ; on the other hand, the hind limbs 

 exceed the fore much more than in Dolichotis, in which the anterior and 

 posterior extremities are of nearly equal length. The gait, it may be inferred 

 from the structure of the feet, was completely digitigrade. In brief, it 

 would hardly be inaccurate to describe Eocardia as a smaller, lighter and 

 shorter-limbed Dolichotis. 



In the following comparative table the distance from the occipital con- 

 dyle to the premolar, inclusive, is taken as 100 and the other dimensions 

 are calculated in percentages of that distance. This standard is chosen 

 rather than the entire length of the skull, because it eliminates the differ- 

 ent proportions of the rostrum. 



MEASUREMENTS. 

 Schistomys 

 ellipticus, 

 Distance, occipital condyle to pA inclusive 100 (49 mm.) 



Scapula length 109.6 



Pelvis, length 



Humerus, length 1 26. 5 



Radius, length 



Ulna, length 



Metacarpal III, length 



Femur, length from great trochanter. . . 171.4 



Tibia, length 175-5 



Tarsus, length 



Metatarsal III, length 63.2 



Phalanx I, digit III, length 



Relationships. Though Eocardia is probably not ancestral to any 

 existing genus, it is, nevertheless, a type of great interest and importance, 

 for it brings before us, in somewhat modified shape, the common ancestral 

 form of Dolichotis and Cavia and possibly even of Hydroch&rus also. 

 In comparing the two former genera, we see that Cavia has the more 

 highly differentiated dentition and Dolichotis the more specialized skull, 

 limbs and feet. Eocardia shows the beginning of the Cavia type of 

 grinding teeth in the shallow accessory enamel folds and in the presence 

 of cement. In the latter, however, only one such fold is deepened and 

 made permanent in each tooth, while Eocardia has three, and this gives 

 at least a hint of the manner in which the highly complex molars of Hy- 

 drochcerus have arisen ; in Dolichotis the teeth have been simplified by the 



