400 



are rudimental in the anterior lumbar, and progressively increase to the last of that series of 

 vertebrae. The clavicles are entire. The radius and ulna are firmly united to each other. 

 There is a third trochanter in the femur. Nearly the distal half of the fibula has coalesced 

 with the tibia. The pollex is shorter than the metacarpal of the index, but the hallux is 



longer than the metatarsal of the second toe. 



Mus. Gould. 



Genus Hapalotis. 

 Dental formula as in Mus. 



2242. The skeleton of the White -footed Australian Rat (Hapalotis albipes). 



The vertebral formula is : 7 cervical, 1 3 dorsal, 7 lumbar, 2 sacral, and 30 caudal. The 

 tubercle of the first rib abuts against the diapophyses of the last cervical and first dorsal ver- 

 tebrae. The pleurapophysis of the sixth cervical extends backwards to the neck of the rib. 

 The second dorsal is characterized, as in other Muridee, by the superior length of its spine. 

 The space between the tenth and eleventh dorsal is that towards which the spines of the 

 trunk-vertebra? converge. The accessory tubercle projects distinctly above the diapophysis 

 of the eighth dorsal, and divides in the eleventh, the metapophysis overlapping the posterior 

 zygapophysis of the tenth dorsal. The anapophyses continue distinct upon the four anterior 

 lumbar vertebrae, the diapophyses of which are better developed than in the Common Rat. 

 Seven pairs of ribs directly join the sternum, which consists of six bones. The clavicles are 

 entire. The humerus is perforated between the condyles. The radius and ulna are moveably 

 united. There is a third trochanter : the distal half of the fibula coalesces with the tibia, 

 except at its extremity. The back part of the mastoid is perforated. The back part of the 

 squamosal is notched, and there are two vacuities in the cranial walls above the tympanic. 

 The temporal muscle has left a shallow indentation on the side of the squamosal. The super- 

 orbital ridge is well marked, and the frontal surface is slightly concave. There is a strong 

 antorbital process, and the antero-inferior root of the zygoma sends forward a broad sharp 

 plate along the outside of the antorbital vacuity. The canal external to the incisive alveolus 

 opens above in advance of this plate. There is a tubercle at the lower angle of the antorbital 

 vacuity. The interparietal is a transverse subquadrate bone. The coronoid process is barely 

 indicated. The dental formula accords with that of the genus Mus, to which all the leading 

 characters of the skeleton prove the close affinity of the Hapalotis. 



Mus. Gould. 



Genus Hydromys. 



Dental formula : i |=|, p j|, m l -~ = 12. 



2243. The skeleton of the Australian Water Rat (Hydromys chrysogaster). 



The vertebral formula is : 7 cervical, 14 dorsal, 7 lumbar, 2 sacral, and 30 caudal. The 

 vertebral artery, after piercing the transverse process of the atlas longitudinally and vertically, 



