368 Annals of the Carnegie Museum. 



Turning to the lateral aspect of the skull in hand, it will be ob- 

 served from fig. 5 of Plate XVI that the " interorbital septum " ex- 

 hibits large vacuities in it, both centrally and above ; though in most 

 skulls of this species the foramen rotundiim is entire — that is, sur- 

 rounded by bone. 



While protected posteriorly by the flaring os squamosum, the en- 

 trance to the ear is much exposed in front, affording the opportunity 

 to fully examine its interior structure and the articular facet for the 

 OS quadratum. Anteriorly, the large quadrilateral pars plana is thor- 

 oughly coossified for its entire outer boundary and above with the big 

 lacrymal hone, and the latter likewise, superiorly and anteriorly, with 

 the frontal and nasal of the same side. Here is a point that at once 

 distinguishes the skull of this extinct Petrel from the skull of a 

 Shearwater of the genus Puffinus; for in the latter group we always 

 find the lacrymal hone to be a free element which promptly comes 

 away during the process of maceration. In ^strelata it is deeply 

 grooved antero-posteriorly at its middle, and in this groove we always 

 find a large, circular, pneumatic foramen, the bone extending out- 

 wards and backwards just below it. Dapfion capense has a lacrymal 

 and a pars plana essentially agreeing with what I have just described 

 for the subject in hand. 



Between the lacrymal and the posterior sharp edge of the nasal 

 of the same side no bony wall exists; so that, when viewed upon this 

 direct lateral aspect, one can look tliroitgJi the skull over the broad 

 vomer below, as is well shown in fig. 5 of Plate XVI ; in other words, 

 the midposterior part of the rhinal chamber is entirely lacking in 

 osseous, protecting, lateral walls. 



At the side of the superior osseous mandible beyond this the sur- 

 face is extensive and smooth, with its lower tomial edge cultrate to 

 the apex beyond. 



A quadrate bone has a broad orbital process, with a markedly 

 truncate extremity; and at the base of this, internally, we always find 

 a single, circular, pneumatic foramen of some considerable size. 

 Above the articular head has two very independent articular facets, 

 each of an ellipsoidal form — the outer being the larger of the two. 



Oct., 1888, XXIII, n. s., Vol. Ill, PL II, fig. 8. Other skulls or marine 

 bird-forms are figured in this part of the work in question, which can be 

 compared with the skull of our Petrel with advantage. 



