TRANSACTIONS OF SECTION D. — DEPT. ZOOLOGY AND BOTANY. 555 



The fifth Linnaean order, Pecora, is a fairly natural group, equivalent to 

 Cuvier's Ruminantia ; but it is no longer considered of the value of an order, since 

 the animals composing it have now been shown to be as closely related to certain 

 of those belonging to the next order as they are to each other. The first genus, 

 Camelus, contains both the American Lamas and the Old World camels, the 

 demonstration of the common origin and close affinities of which has been one of 

 the important results of the recent discoveries in the palaeontology of the Western 

 continent. In the next genus, Moschus, were placed the well-known musk deer of 

 the highlands of Central Asia, and two small African antelopes, which have no 

 special affinity with it. The subsequent inclusion in the same genus of the small 

 chevrotains (Tragulhue), which was very natural at the time, as they agree per- 

 fectly with the musk in the absence of horns and the presence of large canine tusks, 

 by which artificial characters the genus was defined by Linnaeus, was one of those 

 unfortunate associations which has greatly retarded the progress of knowledge of 

 the true affinities of the group. Judging by the popular works on Zoology, it is 

 still as difficult to apprehend that a chevrotain is not a musk deer, as it is that a 

 manatee is not a cetacean ; both errors of the same kind, if not quite so gross, as 

 that of regarding a whale as a fish, or a bat as a bird. The genus Cervus contains 

 six species of true deer, including the moose, reindeer, red deer, fallow and roe, 

 associated with the giraffe. 



The twenty-one species at that time recognized of the great group of 

 hollow-horned" Ruminants are distributed quite artificially in three genera, 

 Capra, Ovis, and Bos. Though subsequent investigations have greatly increased 

 the number of species known, we are still in much uncertainty about their mutual 

 affinities and generic distinctions. Being a group of comparatively modern origin, 

 and only just attaining its complete development, variation has chiefly affected the 

 less essential and superficial organs, and the process of extinction of intermediate 

 forms has not operated sufficiently long to break it up into distinctly separated 

 natural minor groups, as is the case with many of the older families, which yield, 

 therefore, far more readily to the needs of systematic classification, especially as 

 long as the extinct forms are unknown or ignored. 



The sixth order of land mammals, Belltj^e, corresponding to the Pachydermata 

 of Ouvier, contains what is now known to be a heterogeneous collection, viz. the 

 horses, the hippopotamus, the pigs, rhinoceros, and tbe rodent capybara. The 

 abolition of these two last orders and the entire re-arrangement of the ungulate 

 mammals, into two different natural groups, now called Artiodactyla and Perisso- 

 dactyla, first indicated by Ouvier in the ' Ossemens fossiles,' from the structure of 

 the limbs alone, and afterwards confirmed by Owen from comparison of every part 

 of the organization, has been one of the most solid advances made in our knowledge 

 of the relations of the Mammalia during the present century. 



The past history of this, as of so many other groups of vertebrated animals, 

 has been brought to light in an unexpected manner by the wonderful discoveries of 

 fossil remains made during the last ten years in the Rocky Mountains of America ; 

 discoveries, the importance of which will only be fully appreciated when the 

 elaborate and beautifully illustrated work which Professor Marsh has now in 

 progress, is completed. 



The last Linnaean order, Oete, is exactly conterminous with the order so named,. 

 or rather more generally modified to Cetacea, in the best modern systems, for 

 Linnaeus did not commit the error of Ouvier and others, of including the Sirenia 

 among the whales. His knowledge of the animals composing the group was neces- 

 sarily very imperfect, indeed it is only within the last few years, especially since the 

 impulse given to their study by Eschricht of Copenhagen, that the great difficulties 

 which surround the investigation of the structure and habits of these denizens of 

 the open sea have been so far surmounted that we have begun to obtain clear views 

 of their organization, affinities, and geographical distribution. 



Two most remarkable fonns of mammals, so abnormal in their organization as 

 now to be generally considered deserving the rank of a distinct sub-class, the Echidna 

 and Ornithorhynchw, were first made known to science in 1792 and 1799 respectively, 

 and consequently have no place in the Systema Naturce. The very recent discovery 



