]899.] OSTEOLOGY OF THE PYGOPOBES. 1043 



Group 6. (Type P. fluviatilis.) Temporal fossa ill-defined; cerebral pro- 

 minence small ; fossa for insertion of temporalis muscle not deeply 

 excavated on postorbital region of frontals ; with a small postorbital 

 process; upper jaw not longer than cranium. 



Podicipes. 

 B. With abroad bifid, overhanging postorbital process ^.chmcyphorus. 



B. Vertebrje. 



Emargination of neural arches of cervical vertebrae caudad, slight, never 

 extending forward beyond the level of the postzygapophyses ; anterior cervical 

 ribs of great length ; all cervicals save atlas and axis with a bony vertebrarlerial 

 canal closed externally by the cervical ribs; synsacrum elongated, and laterally 

 compressed, so as to be almost styliform. 



A. Neural spines of anterior cervicals in form of long median ridge; hjpera- 



pophyses of anterior cervicals widely separated ; neural arch of 2nd, 3rd, 

 and 4th with a rounded free posterior border. All thoracic vertebraj free, 

 the lst-3rd with long J_-shaped hypapophyses; 6 free caudals, excluding 

 the pygostyle; pygostyie bi-oad and sti-ong CoLYMBiuiE. 



B. Neural spines of anterior cervicals almost obsolete : catapophyses of anterior 



cervicals meeting in the middle line ; last cervico-thoracic and thoracic 

 1-4 anchylosed ; free end of hypapophyses scarcely, if at all, laterally 

 expanded ; 7 free caudals, excluding pygostyle ; pygostyle feeble. 



PODICIPEDIDJE. 



It is almost impossible to distinguish, in the synsacrum, lumbar, lumbo- 

 sacral, and sacral vertebrse. The lumbar region has apparently undergone a 

 great shortening. There are no vertebrae which can be distinguished — in the 

 dried skeleton — as sacral. The postsynsacral region — that lying behind the 

 acetabulum — is of great length. 



The vertebral formula must therefore stand as follows: — 



Syn. sc. 



Cv. 13. Cv. th.l. Th.6+2. L. Lb. sc. Sc. ?5. Cd.lO-f7 = 44. 



8 17 



Colymhidce. 

 Syn. sc. 



Cv.20. Cv. th. 2. Th.6-t-l. L. 4. Lb.sc.S. Sc.2. Cd.6-|-7=51. 



7 13 



Podkipedidte. 



C. Sternum and Pectoral Girdle. 



Corpus sterni with a pair of notches posteriorly ; coracoid grooves deep ; 

 metasternum either notched posteriorly, or broadly linguiform, and projecting 

 far beyond posterior lateral processes ; anterior lateral processes not projecting 

 forwards beyond the level of the coracoid grooves ; no supracoracoid foramen ; 

 clavicle not articulating by a glenoid suriace with acromion of scapula. 



A. Greatest width of sternum across anterior latei-al processes rather less than 

 \ the length ; coracoid groove moderately deep ; spina externa sessile and 

 bifid ; keel very shallow ; metasternum linguiform, projecting far beyond 

 level of posterior lateral processes ; precoracoid very small ; posterior lateral 

 processes of coracoid large and spinose Colymbid-e. 



