OCR Text |
Show 406 MR. W. P. PYCRAFT ON T H E [Mar. 21, b'. Width of interorbital region of the frontals exceeding I that of the frontals between the lachrymals ; pterygoid ends of the palatines gently widening from behind forwards Thalassoyeron. 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. Phxbetria. B. VERTEBRA. All the presynsacral vertebra; 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 cervicals from the 2nd bear ribs in the form of elongated and very slender styles, they become free and bear a distinct capitulum and tubercuium on the last 3 vertebras (cervico-dorsals); the free caudal vertebi'ae bear distinct intercentra, and in the larger species the neural arch of each is provided with a pair of processes 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 vertebra; bear elongated hypapophyses, of which the cephalad are bifid Procellariidce. B. Thoracic vertebrae without hypapophyses Diomedeidce. C. STERNUM AND PECTORAL GIRDLE. The posterior border of the sternum maybe either notched or entire. In the former the anterior coracoid border is produced forwards beyond the level of the anterior lateral process. In the latter the anterior coracoid border does not project far forwards. The base of the coracoid 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 Procellariidce. a-. Coracoid grooves forming markedly oblique angles with the long axis of the sternum ; base of coracoid more than *- 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 Procellaria. b". Hypocleideum long. a3. Width of posterior border of sternum = length of long axis of sternal plate; carina unfenestrated Cymodroma. b3. Carina fenestrated ; posterior border of sternum wider than length of long axis Fregetta. c3. Carina fenestrated; with posterior border of sternum less than long axis; anterior lateral process only slightly projecting above the base of the coracoid ; width of base of coracoid falling far short of length of its long axis Oceanites. d3. Metasternum projecting beyond the posterior lateral processes; carina fenestrated ; anterior lateral processes projecting considerably over the base of the coracoid ; width of coracoid at base nearly equal to the length of the shaft; width across posterior border of sternum less than its long axis Pelagodroma. |