PHTLOGENY OF THE PAL.EOaXATH.^ AND NEOGNATH^. 275 



Key to tlie Species. 



Struthio. 



a. Middle region of anterior border straight or slightly arched ; length of 



eoracoid groove greater than distance between articulations of sternal 

 ribs 1-5. 

 a' . Posterior lateral pi'occsses long and spatulatc, with an extensively ossified 



metasternal region between the jjosterior lateral processes S. niolybdophanes. 



b' . Posterior lateral processes moderately long ; ossified metasternal region 



between posterior lateral processes small S. camelns. 



b. Middle region of anterior border of sterniim sinuous ; posterior lateral pro- 



cesses not spatulate ; no projecting metasternal region between the 



posterior lateral processes ; length of eoracoid groove less than the 



distance between the articulations of sternal ribs 1-5. 

 c'. Width between the free end of the anterior lateral processes much greater 



than the width across their bases B. itieridionalis. 



d'. Width across free end of posterior lateral processes about equal to the 



width across their bases S. australis. 



Rhea. 



a. Anterior border of sternum between the eoracoid grooves slightly excavated ; 



■width between right and left eoracoid grooves greater than length of 



articular surface for eoracoid ; articular surfaces for sternal ribs i . . . R. amencana. 



b. Outer border of sternum between the eoracoid grooves deeply excavated ; 



width between right and left eoracoid grooves equal to or less than length of 



articular surface for eoracoid ; articular surfaces for sternal riljs !• . . . R. macrorhyncha. 



' DrOMjEUS. 



a. Length 6^ in. Coracoid grooves distinct and the sternal protuberance but 



slightly developed -D. novcB-hollmdia. 



b. Length not exceeding 3^ in. ; eoracoid grooves obsolete ; the ventral lip of 



rio-ht side onlv represented ; sternal protuberance conspicuous D. uter. 



Casuarius. 



A. With a pair of low, median, keel-like ridges lying immediately behind a line 



drawn across the sternum immediately behind the coracoid grooves, without 



median pneumatic cavity between the coracoid grooves C. wiappendiculatus. 



B. Without paired median ridges ; with large pneumatic cavity between the 



eoracoid grooves. 

 a. Coracoid grooves deep, the lower lip strongly marked when seen from 

 above; pneumatic cavity very large, extending backwards into a low 

 swollen protuberance lying in the middle line of the sternum between 

 the coracoid grooves. 



