The ROCKY MOUNTAIN PIKA (_Lagomys princeps_) is a small species from six inches to seven and a half inches long, of a greyish-brown colour above, yellowish-brown on the sides, and greyish below. It received its specific name from its discoverer, Sir J. Richardson, in allusion to the name of “Little Chief Hare” given to it by the Indians. It inhabits the summits of the Rocky Mountains from Colorado northwards far within British America, and also occurs in the mountains of Utah, California, and Oregon. Mr. Allen describes its habits as follows:--“The animals are everywhere found in communities, living among the loose rocks from a little below timber-line nearly up to the snow-line. They appear to rarely wander many yards from their homes; are timid, yet easily become familiar. Though retreating to their homes when first alarmed, they soon come cautiously out one after another, till one may hear their sharp little cries in every direction. Their colour so nearly resembles that of the rocks they live among, that they are not easily seen, and their cry is of such a character as easily to mislead one in respect to the point from which it proceeds, seeming to be far away when only a few feet distant. They sit erect, like little Marmots.... They carry into fissures of the rocks large quantities of grass, which they lay up for winter consumption.” CHAPTER V. FOSSIL RODENTIA. Families of Rodents represented by Fossil Remains--State of the “Record of the Rocks”--THE SCIURIDÆ--Sciurine Genera now Extinct--No Fossil ANOMALURIDÆ and HAPLODONTIDÆ--ISCHYROMYIDÆ--_Pseudotomus hians_--_Gymnoptychus_--CASTORIDÆ--Mr. Allen’s CASTOROIDIDÆ--THE MYOXIDÆ--No Fossil LOPHIOMYIDÆ--THE MURIDÆ--THE SPALACIDÆ--THE GEOMYIDÆ--THE DIPODIDÆ--THE THERIDOMYIDÆ--THE OCTODONTIDÆ--THE HYSTRICIDÆ--THE CHINCHILLIDÆ--THE DASYPROCTIDÆ--THE CAVIIDÆ--THE LEPORIDÆ--THE LAGOMYIDÆ--_Mesotherium cristatum_--Difficulties concerning it--Mr. Alston’s Suggestion--THE HEBETIDENTATA--Teeth--Skull--Skeleton--Conclusions regarding it--Table of Rodent Families--Concluding Remarks.