1 ^'^ 



i^;;).] '-'-'" [Cope. 



//. Description of two large extinct rodents from Anguilla, West Indies, 

 with remains of liuman art associated. 



Ambltrhiza, Cope. 



Molai'S curved prismatic, rootless, some composed of four, others of 

 five dentinal columns, separated by more or less transverse plane lami- 

 nae of enamel ; the whole enclosed in a sheath of cementum. The fangs 

 contracted, closing one or more of the dentinal columns at the base. 

 Triturating surfaces plane, subquadrate, or subtrigonal. Incisors nar- 

 row, with very small piilp cavity for much of the length ; anterior plane 

 transverse, the enamel equally folded in a narrow band on the inner and 

 outer faces. Digits subungulate. 



The characters of the genu^s ally these animals to the Chinchillae, and do 

 not present more than a small number of differences, though important 

 ones. Thus the closure of the dentinal columns below, indicates either 

 a limit to the formation and protrusion of teeth of the same degree of 

 complication, or the entire termination of such process, as in the root 

 bearing types. It presents in fact an interesting transition between the 

 monophyodont and diphyodont structures. There are two extinct genera 

 related to the Chinchillae, with which the present may be compared ; 

 Archaeomys Laiz. Par. and Megamys D'orb. The first is said only to 

 differ from Lagidiuni in the presence of an additional dentinal column, so 

 that the form of the root is to be presumed to be the same ; it therefore 

 differs from Amblyrhiza in that respect, as well as in having the dentinal 

 columns | instead of f . The known species are from the fresh-water 

 limestone of Allier, France. Megamys patagoniensis is only known from 

 a tibia and rotula, and its dental characters are therefore not ascertain- 

 able. I cannot refer the present animal to that genus with any proba- 

 bility. The species is much larger than that described by D'orbigny. 



Ambltrhiza intjndata. Cope. Proceed. Acad. Nat. Sci., Philada., 

 1868, p. 313. 



The remains of this large rodent were found in a mass of breccia, which 

 was thrown out in the excavations made in a cavern in the small Island 

 of Anguilla, W. I. The remains occurring in that most eastern region 

 of the West Indian Zoological district, might be anticipated to have a 

 special interest in connection with the history of the submergence of a 

 once great continent. With this impression, the writer examined a quan- 

 tity of the above breccia and cave deposit, which was brought to Phila- 

 delphia as a probably available phosphatic manure. It was found to be 

 valueless for this purpose, and the only result of the outlay was the dis- 

 covery of the Amblyrhiza. Most of the fragments were dressed from a 

 single block. There were in this the extremity of a right femur with 

 patella, shafts of various long bones, fragments of pelvis and maxillaiy 

 bones, with three molars, and two partially complete, and other much 

 broken incisors. The teeth were scattered among the bones, and are so 

 related in size to most of them, as to induce the belief that they all be- 

 long to the same animal. This is strengthened by the occurrence of the 

 A. r. s. — VOL. XI — X 



