401 



pierces the neural arch midway between its fore and hind borders. The pleurapophysis of 

 the sixth cervical is strong, and directed outwards and backwards beneath the diapophysis of 

 the seventh. This vertebra has no pleurapophysis, and its transverse process is, therefore, 

 imperforate. The first rib of the dorsal vertebrae is unusually short. The second dorsal ver- 

 tebra is remarkable, as in other Muridae, for the height and strength of its spine, which has 

 a rough obtuse termination, as if for the attachment of an epiphysis. The spine of the 

 eleventh dorsal is that towards which those of the other trunk-vertebrae converge. The 

 accessory process divides on the twelfth vertebra, and the metapophysis and anapophysis are 

 distinct on the five following. The anapophysis is obliterated in the last four lumbar ver- 

 tebrae. The transverse processes of the caudal vertebrae are. remarkable for their antero- 

 posterior extent, and give an oblong quadrate form to the vertebrae in the middle of the tail : 

 in the posterior caudal vertebrae these processes become notched on either side. Most of the 

 caudal vertebrae have strong haemapophyses, and the whole forms the basis of a powerful 

 natatory organ. Eight pairs of ribs directly join the sternum, which consists of seven bones. 

 The clavicles are entire. The deltoid ridge projects from the fore part of the proximal half 

 of the humerus, and is prominent below. The humerus is imperforate. The ulna sends a 

 process to abut against the radius across the middle of the interosseous space. The fore-foot 

 is pentadactyle, but the pollex does not exceed the length of the metacarpus of the index. The 

 femur has a third trochanter and a fabella behind each condyle. The distal third of the 

 fibula has coalesced with the tibia. The hallux extends to the second phalanx of the next 

 toe. The strength of the hinder half of the skeleton, with the size of the hind extremities, 

 contrasts with the sleuderuess of the fore part. 



Hunterian. 



2244. The skull of the Hydromys chrysogaster. 



The teeth of the right side of the upper and lower jaws are separately displayed. The 

 ribs are exposed in situ. 



Hunterian. 



2245. The skull of a female Hydromys ckrysogaster . 



The cranium is broad and depressed, smooth and slightly convex above : the interparietal 

 is semicircular. A crescentic opening is left between the broad posterior part of the squamosal 

 and tympanic. The auditory bulla is of moderate size. The outer border of the antorbital 

 aperture is not produced forwards, as in the true Rats and the Arvicolidae, and the aperture 

 of the canal external to the incisive alveolus is larger and more conspicuous. The malar bone 

 is unusually small, compressed, styliform, and suspended between the roots of the zygomatic 

 arch. A distinct tubercle projects from the lower end of the antorbital hole. 



Presented by the Natural History Society of Calcutta. 



3 F 



