40G MK. w. p. PYCEAi'T ON THE [Mar. 21, 



h'. Width of interorbital region of the frontals exceeding \ that of the 

 frontals between the lachrymals ; pterygoid ends of the palatines gently 

 widening from behind forwards Thalassogeron. 



b. Interorbital region of frontals reduced to a narrow median ridge ; antorbital 

 plate extending outwards to the level of or beyond the outer border of the 

 lachrymal ; no tubercle between the mammillary processes. Phoebetria. 



B. Veetebb^, 



All the presynsaeral vertebrre are free and heteroccelous ; the centra of the 

 thoracic bear more or less conspicuous lateral depressions and are often highly 

 pneumatic ; only the 2nd-5th or 6th cervicals bear neural spines ; all the cervi- 

 cals i'rom the 2nd bear ribs in the form of elongated and \ery slender styles, 

 they become free and bear a distinct capitulum and luberculum on the last '6 

 vertebrse (cervico-dorsals) ; the free caudal vertebric bear distinct intercentra, 

 and in the larger species the neural arch of each is provided with a pair of 

 procCEses directed forwards and embracing the neural spine of the vertebra 

 next in front; catapophyses of cervicals never meeting in mid-ventral line to 

 form a canal. 



A. Many if not all the thoracic vertebrae bear elongated hypapophyses, of 



which the cephalad are bifid PrvcellariidcB. 



B. Thoracic vertebras without hypapophyses Diomcdeida. 



C. Steknum and Pectoral Giedle. 



The posterior border of the sternum maybe either notched or entire. In the 

 former the anterior coraeoid border is produced forwards beyond the level of 

 the anterior lateral process. In the latter the anterior coraeoid border does 

 not project far forwards. The base of the coraeoid is always of great width, 

 and the furculum articulates by ligament with the antero-ventral angle of the 

 carina. 



A. Pneumatic foramina of the dorsal surface of the sternum, when present, 

 never very conspicuous, and confined to the anterior region of the middle 

 line ; carina sharply defined throughout the whole length of the sternal 

 plate; spina interna absent ProcellaritdeB. 



a, Coraeoid grooves forming markedly oblique angles with the long axis of 

 the sternum ; base of coraeoid more than i as broad as long ; articular 

 surfaces of sternal ribs extending backwards far beyond the anterior 

 lateral processes. 

 a'. Posterior border of the sternum entire ; clavicle with a hypocleideum ; 

 spina externa pointed. 

 a" . Hypocleideum small ; width of posterior border of sternum much less 



than its long axis Frocellaria. 



b". Hypocleideum long. 



a^. Width ofposterior border of sternum = length of long axis of sternal 

 plate; carina unfenestrated Cymodroma. 



b^. Carina fenestrated ; posterior border of sternum wider than length 

 of long axis Freyetta. 



<^. Carina fenestrated ; with posterior border of sternum less than long 

 axis ; anterior lateral process only slightly prujeeting above the 

 base of the coraeoid ; width of base of coraeoid falling far short 

 of length of its long axis Occanites. 



d^. Metasternum projecting beyond the posterior lateral processes; 

 carina fenestrated ; anterior lateral processes projecting con- 

 siderably over the base of the coraeoid ; width of coraeoid at base 

 nearly equal to the length of the shaft ; width across posterior 

 border of sternum less than its long axis Pelagodroma. 



