6l2 



NATURE 



[Oct. 25, 1888 



and this induces a great danger of founding species or 

 higher groups upon the evidence of upper jaws, which 

 cannot be decisively shown to be distinct from those 

 founded upon the evidence of the mandibles. Prof. 

 Osborn, as will be noticed below, has not altogether 

 steered clear of this danger ; and we consider it would 

 be advisable in delicate researches of this nature to lay 

 down a rule that family or higher groups should only be 

 formed upon the evidence of homologous parts, even if 

 genera and species have been named upon the evidence 

 of dissimilar parts of the skeleton. 



Before, however, proceeding to any detailed criticism, 

 it will be advisable to take a brief survey of the memoir 

 before us, and to note the scheme of classification which 

 is proposed. The memoir begins with a survey of 

 previous work on the subject, especial attention being 

 directed to the labours of Sir Richard Owen in Europe, 

 and to those of Profs. Cope and Marsh in America. On 

 the second page (187) a table is given of all the 

 described genera of Mesozoic Mammals, which include 

 forms from Europe, America, and South Africa ; 

 together with certain allied Tertiary genera from North 

 America and France, and Thylacoleo of the Pleistocene of 

 Australia. We may add that since this memoir was 

 sent to press, forms allied to those of the North American 

 Eocene have been described by Sefior Ameghino in the 

 Tertiaries of the Argentine Republic. The next section 

 is devoted to a detailed description of the British forms, 

 in which certain generic terms, proposed by the author 

 in a preliminary communication, are fully described and 

 illustrated. We may here mention that the author tells 

 us that the process of passing his memoir through the 

 press occupied an unusually long period, during which 

 certain other memoirs appeared on the subject ; and that 

 he thus saw occasion to modify in some respects several 

 statements made in the earlier part of the work, footnotes 

 being usually appended to this effect. 



After the descriptive portion we come to what is really 

 the most important section of the whole memoir — namely, 

 that headed the classification and zoological relationships 

 of the Mesozoic Mammalia. It is here observed that 

 these forms may be divided into two large groups. " In 

 the first group, A, one of the incisors is greatly developed 

 at the expense of the others, and of the canine, which 

 usually disappears ; behind these teeth is a diastema of 

 varying width, followed by premolars which are subject 

 to great variation in form and number, while the molars 

 bear tubercles. In the second group, B, the incisors are 

 small and numerous, the canine is always present and 

 well developed ; the teeth usually form a continuous 

 series, and the molars bear cusps instead of tubercles." 

 These two groups are compared to the Diprotodontiaand 

 Polyprotodontia, among existing Marsupials, and the 

 following scheme of classification is proposed : — 



A. First Group. 



I. Sub-order Multituberculata. 



1. Family Plagiaulacid^e. — Microlestes, Plagiaulax, 



Ctenacodon, Ptilodus, Neoplagiaulax, Meniscoessus, 

 and perhaps Thylacoleo. 



2. Family Bolodontid/E. — Bolodon, Allodon, and 



perhaps Chirox. 



3. Family Tritylodontid.e. — Tritylodon, Triglyphus, 



4. Family Polymastodontid^e. — Poly mastodon. 

 Incertce sedis —Chirox. 



B. Second Group. 



I. Order Protodonta. 



Family Dromatheriid^e. — Dromatheriitm, Micro- 

 conodon. 



II. Sub-order Prodidelphia. 



1. Family Triconodontid/e. — Amphilestes, Amphitylus, 



Triconodon, Priacodon, Phascolotherium, Tinodon, 

 Spalacotherium, Menacodon. 



2. Family AMPHITHERIID^. — Amphitherium, Dicrocy- 



nodon (Diplocynodon), Docodon, Enneodon, Peramiis. 



3. Family Peralestid^:. — Peralestes, Peraspalax, 



Paurodon. 



4. Family Kurtodontid^;. — Kurtodon. 



III. Sub-order Insectivora Primitiva. 



1. Family Amblotheriid^. — Amblotherium, Achy- 



rodon. 



2. Family Stylacodontid^;. — Stylacodon, Phascolestes, 



Dryolesles, Asthenodon. 

 Incerto? sedis — Laodon. 



The Multituberculata, excluding Thylacoleo, extend in 

 time in Europe and North America from the Upper 

 Trias to the Lower Eocene, but the recently discovered 

 South American forms may be of later age. In dis- 

 cussing the relationship of this group of families on 

 p. 212, the author states that, admitting their Mar- 

 supial relationship, it is clear that the genera " are closely 

 related to each other, and widely separated from the 

 Diprotodontia by their dental structure, which is very dis- 

 similar, and indicates that they probably branched off 

 from the stem of the recent Marsupials at a remote period, 

 probably I the Triassic." They are accordingly regarded 

 on the following page as a sub-order of Marsupials, 

 characterized by the tuberculated characters of their 

 molars. If, however, as suggested on p. 214, Thylacoleo, 

 which is evidently only an aberrant and specialized 

 Phalanger, has any sort of relationship to the Plagi- 

 aulacida, then it will be evident that this group cannot 

 be even subordinate^ separated from the Diprotodonts 

 Further observations upon the relationships of this group, 

 are given upon pp. 251 and 254, the latter section having 

 evidently been written subsequently to the earlier sections. 

 On the former page evidence is adduced to show that in 

 some of these forms the first upper incisor has been lost, 

 and the second becomes hypertrophied, whereas in ex- 

 isting Marsupials it is the first which always persists and 

 becomes enlarged. There is no evidence as to the serial 

 homology of the lower incisor. On p. 254 and the 

 following pages, the suggestion of Prof. Cope, based on 

 the resemblance of the molars of the Multituberculata to 

 the aborted teeth of Ornithorhynchus, that these forms 

 maybe Monotremes,is discussed at some length, but with- 

 out any definite conclusion being reached. We presume, 

 however, that in writing this part of the memoir the 

 author had come to the conclusion that the relationship 

 of these forms to Thylacoleo is altogether a myth. It is, 

 however, at first sight not very easy to believe that the 

 general similarity in the structure of the cutting fourth 

 premolar in the Multituberculata and the modern Diproto- 

 dontia is not indicative of a real affinity between the two ; 

 and as to the argument that the peculiar structure of the 

 two molars is of itself sufficient to indicate the sub- 

 ordinal distinction of the Multituberculata, we think that 

 a sub-order which contains such different types of molar 

 I dentition as are shown by Macropus, Pseudochirus, Phas- 



