io8 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XIV. 



the flat side. The processus brevis at the base of the manubrium is 

 relatively insignificant. The processus gracilis has two thin longitudinal 

 ridges bounding a long v-shaped groove which seats the tympanic ring. 

 The extremity of the process is somewhat expanded and obtuse. The 

 union with the tympanic is close and considerable care is required in 

 forcing the parts away from each other. The malleus differs from that 

 of Perameles (P. bougainvillei} principally in its shorter neck; from that 

 of Didelphis it is distinguished by its generally frailer construction and 

 its closer union with the tympanic. 



The incus is practically identical with that of Perameles, differing 

 mainly in the processus brevis which is somewhat compressed and 

 truncate instead of long and conical. The processus longus is very 

 slender distad of the sharp right angle at which it is bent. The Sylvian 

 apophysis is elliptical. The incus in adults is rather firmly attached to 

 the malleus and does not separate except after slight pressure. 



The stapes is strictly columelliform without trace of an opening and 

 there is not even an appreciable difference in its diameter from the head 

 to the base. The head is very small and the base relatively large and 

 elliptical. In adults, the stapes is well ossified. 



The auditory ossicles of Ccenolestes are clearly of a type closely 

 approaching that of Perameles, which was regarded by Doran (1879) as 

 the lowest among marsupials. They also show resemblance to some 

 of the dasyures, which, as described by Doran, have the stapes columel- 

 liform. Whether this simple stapes is in truth a primitive character or 

 not, it serves at least to distinguish Ccenolestes sharply from the didel- 

 phids, in which the stapes is always bicrurate. So far as the auditory 

 ossicles are concerned, therefore, Ccenolestes resembles Australian rather 

 than American forms and especially approaches the peramelids and 

 dasyurids. 



Mandible. The mandible is slender and relatively straight ante- 

 riorly, its greatest curvature being just below the base of the coronoid 

 process. The symphysis is long but weak. The rami have exceptionally 

 little divergence. The coronoid is large, broad, and nearly upright. Its 

 anterior border is gently curved but approaches the vertical more closely 

 than in any polyprotodonts. The broad masseteric fossa, is rather shal- 

 low and is indistinctly divided into an anterior and a posterior portion 

 by a weak elevation between the tips of the coronoid and the condyle. 

 Near the lower edge of the masseteric fossa is a tiny foramen, indistinct 

 in some specimens, but obvious in others. A similar foramen is found 

 in many Australian diprotodonts but does not occur in polyprotodonts. 

 Its presence in Abderites and Garzonia has been noted by Ameghino and 

 Sinclair. Mental foramina of the usual character are present, a larger 



