of the Genus Stenomylus. 



309 



developed as wings to either side arid about halt* the length of 

 the centrum, the outer margin being prolonged fore and aft 

 and thickened. The wide posterior facet is placed obliquely 

 to the length of the centrum, indicating a marked upward 

 bend to the neck, so it is fair to conclude that the head was 

 carried high. On the rear there are facets for the first ribs. 



From the foregoing it is clear that this genus in such deep- 

 seated characters as the position of the vertebrarterial canal, the 

 reduction of the neural spines, and the characters of the trans- 

 verse processes, relates itself closely to the Tylopoda, having 

 especial affinity to the primitive genus Poebrotherium. 



The following measurements give the relative sizes of the 

 various vertebras in the three known species and in Poe- 

 brotherium. 



Length of Centrum X Width of Vertebra. 





1st. 



2d. 



3rd. 



4th. 



5th. 



6th. 



7th. 



tS. hitchcocki 



j 33 long 

 ( 39 wide 



54 



29 



68 

 4~l 



58 

 37 



54 



37 



49 



37 



35 

 40 





( 35 



62 



67 



54 





48 





S. crassipes 



) 57 



33 



35 





38 



45 





IS. gracilis 











75 



72 





P. ivilsoni 



j 36 



r 



66 



63 



58 



56 



45 



36 



of twelve 

 Fig. 13. 



Dorsal vertebrw. — The dorsal series consists 

 vertebras, measuring 242 mm . The neural 

 spines are all wide thin plates, so closely 

 set in front as to leave almost no inter- 

 vals between vertebras, and reaching a maxi- 

 mum in height on the fifth dorsal, from 

 which point on they are lower with increas- 

 ing intervals between successive spines. 

 The anticlinal vertebra is the eleventh dor- 

 sal. Metapophyses appear first on the 

 eighth dorsal and occur on each successive 

 centrum, situated each time a little higher 

 and further forward, until on the eleventh 

 the metapophysis unites with the prezy- FlG# 13> stenomylus 

 gapophysis and together they make a con- hitchcocki, sixth dor- 

 cave facet which incloses the cylindrical sal seen from the side, 

 postzygapophysis. x / 



Lumbar vertebra — The lumbar series consists of seven ver- 

 tebrae, which total 190 mm in length. Each one is characterized 



Am. Jour. Sci.— Fourth Series, Vol. XXIX, No. 172.— April, 1910. 

 21 



