MAY, 1921. AMERICAN MARSUPIAL, CENOLESTES 'OscooD. 77 



evidence is therefore inconclusive as to whether the normal arrange- 

 ment in Canolestes is bilobate or trilobate. In most marsupials, except 

 the wombat and some of the Macropodidae, it is said to be trilobate. 

 In several specimens which I have examined of Didelphis, Marmosa, 

 and Peramys it is trilobate. In C&nolestes, there is at least a tendency 

 for it to be bilobate. 



Trachea. The tracheal rings are about nineteen in number and are 

 not united dorsally but separated by a broad interspace. 



Larynx. The epiglottis is large and elevated, and has a slight 

 anterior emargination which is most evident in the cartilage after 

 removal of the soft external membranes. It is attached to the thyroid 

 cartilage ventrally. The thyroid is continuous medio-ventrally with 

 the cricoid and its bony wings partially inclose the cricoid laterally. 

 Its anterior or superior horn has ligamentous attachment to the thyro- 

 hyal; its posterior or inferior horn attaches similarly to the outer 

 extremity of the cricoid which is here very slightly ossified. The aryte- 

 noids are large, subtriangular and partially united dorsally. The 

 cartilage of Santorini is developed into a prominent curved protuberance 

 which is continuous with the high muscular crest of the arytenoid 

 which, meeting its fellow of the opposite side, nearly closes the cavity 

 of the larynx with the exception of a very small passage on the ventral 

 side. 



CIRCULATORY SYSTEM. 



Owing to the condition of the material, no attempt was made to 

 study the circulatory system in detail. The heart is as usual in mar- 

 supials. In comparison with that of Didelphis it shows no very important 

 characters. In ventral view the auricles meet over the base of the 

 pulmonary artery, entirely concealing it, whereas in Didelphis it is 

 broadly exposed. The bases of the right subclavian and right carotid 

 are very closely approximated and both join the left carotid scarcely 

 higher than its junction with the aorta. In Didelphis there is an appre- 

 ciable space between the origins of the right subclavian and right 

 carotid. 



SKELETON. 



Plates XI-XVI. 



CERVICAL VERTEBRAE. 

 Plate XI. 



The seven cervical vertebrae are freely movable and distinct. As 

 in the majority of marsupials, the only one having a prominent spinous 

 process is the axis. The neural arches have relatively thin, flattened 



