NATURAL SCIENCES OP PHILADELPHIA. 445 



animals it has a long, narrow form like that of the opossum, and 

 in the first named, where the interior form can be seen, it is evi- 

 dent that the cerebral hemispheres were small and narrow, and that 

 the olfactory lobes were relatively large, and were entirely un- 

 covered, projecting beyond the hemispheres. 



In Ambloctonus, Didymictis, and three undetermined forms, the 

 femur supports a third trochanter. In all the genera the ilium 

 has a well-marked external anterior ridge, which continues from 

 the acetabulum to the crest, distinct from the internal anterior 

 ridge. The ilium has, therefore, an angulate or convex external 

 face, as in Insectivora and Marsupial ia, and does not display the 

 usual expansion in a single plane of most of the placentals. In 

 all the genera there is a strong tuberosity in the position of the 

 anterior inferior spine, which is wanting in the Mammalia, except- 

 ing certain Insectivora and Prosimise, 1 although it marks the posi- 

 tion of the origin of the rectus femoris muscle in all types. 



The glenoid cavity of the squamosal bone is transverse, and 

 well defined anteriorly and posteriori}-, as in the Carnivora. Of 

 the first series of carpal hones of the four genera named, I have 

 been able to learn nothing, but in the genus Synoplotherium from 

 the Bridger Eocene of Wyoming, which probably belongs to this 

 group, the scaphoid and lunar bones are separate and not united 

 as in the Carnivora. 



The above characters point to the Marsupialia or the Insec- 

 tivora as the proper location for the flesh-eaters under considera- 

 tion ; and the evidence is much more weighty in favor of the lat- 

 ter order as their true position. For in the genera Oxysena and 

 Didymictis the posterior part of the inferior border of the mandi- 

 bular ramus is not inflected as in Marsupialia, nor are the ante- 

 rior inferior iliac tuberosity and third trochanter seen in that or- 

 der, while both exist in the Insectivora. 



Cuvier describes 2 the tibia of Carnivora as follows: "Quanta 

 la tete infe'rieure, tous les carnassiers se distinguent de l'homme 

 par sa figure plus etroite du cote externe que le l'interne, et par sa 

 division en deux fosses oblique, an moyen d'une arete arrondie 

 qui repond a la partie de l'astragale. . . Le phoque l'a cepen- 

 dant d'une forme tres-particuliere par l'excessif aplatissement de 

 sa moitie superieure, et par sa facette particulaire inferieure, qui 

 est en concavite simple et pen profounde." 



The astrag-alar articular face of the tibia in the genera above 

 named is not divided into the two oblique fossae by " a rounded 

 crest which is applied to the groove of the superior pull} r -shaped 

 face of the astragalus." It is uninterrupted and more or less ob- 

 lique in the transverse direction ; always so at the posterior bor- 

 der. The inner malleolar process is produced downwards, and 

 rests in a concavity on the inner side of the neck of the astragalus. 



1 See the figure of Solenodon by Peters, and Chiromys by Owen. 



2 Ossemens Fossiles, vii. p. 112. 



