474 University of California Publications in Geology [Vol. 7 



Lutra canadensis 



10 Foramen lacerum posterius 



small. 



11 Neck long, nearly 3/10 length 



of trunk. 



12 Tail with about 24 vertebrae. 



13 Intervertebral foramina small. 



14 Zygapophyses comparatively 



highly developed. 



15 Anapophyses present on all 



the lumbar vertebrae but 

 the fifth and sixth. 



16 Vertebral centra long antero- 



posteriorly, dorso-vent r a 1 

 measurement relatively small. 



17 Epiphyses less developed. 



18 Vertebrarterial foramen of 



atlas small, round; trans- 

 verse process plate-like, 

 thin, expanded; dorsal arch 

 broad antero-posteriorly. 



19 Spine of axis long antero- 



posteriorly. 



20 Vertebrarterial canal of sixth 



cervical vertebra small; 

 transverse process divided 

 into three parts, one lateral 

 peglike, and two ventro- 

 lateral platelike processes. 



21 Transverse process of third 



lumbar vertebra platelike; 

 metapophyses wide; ana- 

 pophyses highly developed. 



22 Sacrum with zygapophyses in- 



dicated; transverse process 

 on piosterior sacral. 



23 Chevron present on fourth 



caudal vertebra. 



24 Bibs light. 



25 Pelvis comparatively light; 



obturator foramen bounded 

 by light bars. 



26 Pelvis forming slight angle 



with vertebral column. 



27 Ilia not markedly flaring 



anteriorly. 



28 Fore limb comparatively 



large. 



29 Olecranon of ulna slightly 



larger than in Latax. 



Latax lutris nereis 



10 Foramen lacerum posterius 



large. 



11 Neck short, less than 2/10 



length of trunk. 



12 Tail with number of verte- 



brae reduced, varying 

 from 18 to 21. 



13 Intervertebral foramina large. 



14 Zygapophyses not so highly 



developed. 



15 Anapophyses present on first 



three lumbar vertebrae 

 only. 



16 Vertebral centra short antero- 



posteriorly, dorso-vent r a 1 

 measurement relatively large. 



17 Epiphyses greatly developed. 



18 Vertebrarterial foramen of 



atlas large, round; trans- 

 verse process heavy; dor- 

 sal arch narrow antero- 

 posteriorly. 



19 Spine of axis short antero- 



posteriorly. 



20 Vertebrarterial canal of sixth 



cervical vertebra large; 

 transverse process divided 

 into three peglike pro- 

 cesses. 



21 Transverse process of third 



lumbar vertebra short and 

 peglike; metapophyses nar- 

 row; anapophyses indicated 

 merely. 



22 Sacrum with no zygapophyses 



indicated; small transverse 

 process on posterior sacral. 



23 Chevron absent from fourth 



caudal vertebra. 



24 Ribs heavy. 



25 Pelvis comparatively heavy; 



obturator foramen bounded 

 by heavy bars. 



26 Pelvis more nearly parallel to 



vertebral column. 



27 Ilia markedly flaring an- 



teriorly. 



28 Fore limb comparatively small. 



29 Olecranon of ulna slightly 



smaller than in Lutra. 



