AXIAL SKELETON OF THE PELECANID^. 355 



ridges : one median, hypapophysial ridge, extending to about the postaxial end of the 

 preaxial two thirds of that surface ; and two lateral, parapophysial ridges (fig. 4, hi/'), ex- 

 tending and diverging postaxiad till each ends in a process on the ventral side of the ex- 

 ternal ventral angle of the postaxial articular surface of the centrum. There thus comes 

 to be a small fossa beneath the postaxial third of the centrum. The postzygapophyses 

 project postaxiad much beyond the postaxial end of the centrum. 



In Plotus novce-hollandice the hypapophysial ridge is more developed, and extends 

 almost to the postaxial end of the centrum, while the lateral ridges are like delicate 

 rib-like styloid processes, there being a defect of ossification in each. 



The THIRD VERTEBRA (Plate LV1II. figs. 5 & 6) is almost half as long again as is the 

 second. It is, like the third of Pelecanus, greatly drawn out, and with the neural spine 

 and hypapophysis all but entirely suppressed. There is no interzygapophysial ridge. 

 The postaxial half of the median hypapophysial ridge is replaced by a narrow, shallow 

 groove, the margins of which must be reckoned as catapophysial, while a parapophysial 

 ridge runs along each side of the ventral surface of the centrum, and ends postaxially 

 in a rib-like styloid process, which begins to project freely ventrad as well as postaxiad 

 at about the preaxial end of the postaxial fourth of the centrum, almost extending 

 postaxiad as far as the preaxial end of the postaxial articular surface of the centrum. 

 A small tubercle (which may be either the representative of a tubercular process or 

 a metapophysis) projects just behind the praezygapophysis and above the tubercle at 

 the preaxial end of the parapophysial ridge. From the former tubercle a slight ridge 

 descends obliquely to join the parapophysial ridge at about its middle. 



The FOURTH VERTEBRA (Plate LVIII. figs. 7 & 8) is about equal in length to the third, 

 and is quite like it, except that the median subcentral groove is a little deeper and 

 extends along the whole length of the centrum. At the postaxial end of the preaxial 

 third of each lateral margin of the subcentral groove a small catapophysial process 

 projects downwards, while between such lateral margin and the more externally situated 

 preaxial part of the parapophysial ridge (p 1 ) is an antero-posterior groove (fig. 8, g) which 

 corresponds with the similarly situated groove beneath the fifth and sixth vertebrae of 

 Pelecanus. The styloid process begins to start out at a point slightly more preaxial. 



The FIFTH VERTEBRA (Plate LVIII. figs. 9-11) is like the fourth, except that it is 

 very slightly shorter, and that the styloid processes are again a little more preaxial, 

 and the postzygapophyses extend postaxiad a little beyond their articular surfaces. 



The SIXTH VERTEBRA (Plate LVIII. figs. 12-14) is decidedly shorter, not greatly ex- 

 ceeding the axis in length ; and here, while the catapophysial margins of the sub- 

 central groove are more raised, the styloid processes are shorter and more preaxial, 

 a wide, subequal, antero-posterior groove extending between the catapophysial and para- 

 pophysial ridges. Here a neural spine begins to reappear 1 , the postzygapophyses are 



* In Plotus novw-liollandice it begins in the fifth vertebra. 



VOL. x. PART vii. No. 6. August 1st, 1878. 3c 



