6 THE VOYAGE OF H.MS. CHALLENGER. 



magellanicus, although well developed posteriorly, it gradually narrows in front and 

 disappears entirely before reaching the lachrymal hone. In Spheniscus mendiculus, 

 Spheniscus minor, Ajitenoclytes, and Pygosceles this ledge of bone does not exist, and 

 consequently in these the supra-orbital groove is much narrower, seeing that it is confined 

 to the lateral borders of the frontal bone, and is not completed externally by the osseous 

 plate met with in the other species above named. 



The breadth of the inter-orbital portion of the frontal bone varies much in different 

 varieties of the same species, and little value can be placed upon this as affording a specific 

 characteristic. In Eudijptes chrysocome from Tristan, as well as from Kerguelen, it is 

 narrow, while in Eudyptes chrysocome from the Falklands, as also in Eudyptes chrysolo- 

 phus it is relatively broad. In Spheniscus magellanicus, Spheniscus minor, Spheniscus 

 mendicidus, and Pygosceles the intermediate plate of the frontal bone is broad, while 

 in Spheniscus demersus it is as narrow as in Eudyptes chrysocome from Tristan. 

 A2)tenodytes, again, agrees with Eudyptes chrysolophus and with Spheniscus magellanicus 

 in having a relatively broad inter-orbital space. 



The nasal bones in every species of Penguin coalesce in the middle line superiorly, 

 and separate completely the ascending processes of the intermaxillary bones from the 

 frontal bone. They are deeply excavated and form the upper, and a portion of the lateral 

 boundaries of the anterior narial apertures. 



These apertures are bounded by the nasal and by the intermaxillary bones. In 

 Eudyptes they present the form of elongated oval slits, whose length is equal to two-thirds 

 of that of the upper jaw. The posterior boundary of each is formed by the nasal bone, 

 and is situated opposite the middle in length of the bony bar which fonns the upper 

 boundary of the lachrymo-nasal fossa. In Spjheniscus, on the other hand, these 

 apertures are of small size, and correspond only to the middle third in length of 

 the beak. In every species of Spheniscus, moreover, with the single exception of 

 Spheniscus minor, the posterior extremities of the narial apertures Lie altogether 

 in front of the anterior border of the lachrymo-nasal fossa — a point which at once 

 serves to distinguish the skull of Spheniscus from that of Eudyptes. Spheniscus minor 

 forms a curious exception to this arrangement, the posterior boundary of the nasal 

 apertures in that bird being situated opposite the middle in length of the lachrymo- 

 nasal fossa as in Eudyptes. In Spheniscus minor, moreover, these apertures are of much 

 larger size than in other species of the genus, and agree both in respect of size and 

 form with those of Eudyptes rather than with those of any other species of Spheniscus. 

 In respect of the form and position of the narial apertures, Aptenodytes and Pygosceles 

 agree with Eudyptes rather than with Spheniscus. In both genera the posterior 

 border of the aperture corresponds to the middle in length of the lachrymo-nasal 

 fossa, and in both the aperture is relatively larger than in Spheniscus. Indeed, by 

 reason of the elongation of the facial portion of the skull in these genera, the 



