10 THE VOYAGE OF H.M.S. CHALLENGER. 



of the latter genus. In Sjiheniscus the inferior inter-ramal space narrows gradually from 

 base to apex of the lower jaw-bone, and the depression which represents the anterior of 

 the two foramina in the lower jaw of Eudijptes, more pronounced than in that genus, 

 forms a well-marked longitudinal groove, which, however, is not perforated. In 

 Spheniscus, moreover, the dentary suture is much more oblique from before backwards 

 than in Eudyptes, and the posterior angular process is relatively longer and more 

 prominent in the former than in the latter genus. 



Spheniscus minor, however, diflfers from its congeners inasmuch as the posterior 

 angular process much more closely resembles that of Eudyptes than that of any other 

 species of its own genus, being shorter and more stunted than in these. 



Pygosceles and Aptenodytes agree with one another and with Eudyptes in the form 

 of the lower jaw-bone. This resemblance is, however, to some extent masked by the 

 greatly elongated form of the lower jaw of these two genera as compared with that of 

 Eudyptes. Still, the form of the jaw as a whole agi'ees more closely with that of Eudyptes 

 than with that of any species of Sp)heniscus. In both Pygosceles and Aptenodytes the 

 dentary suture is more oblique than in Eudyptes but less so than in Spheniscus ; in botli 

 the anterior ramal foramen presents the form of an elongated slit which completely per- 

 forates the ramus, and in both the angular processes resemble those of Eudyptes rather 

 than those of Sjjheniscus. In Pygosceles, however, the posterior angular process is 

 relatively less prominent than in Ap>tenodytes. 



Tlie Hyoid Bone} — The hyoid bone of every species of Penguin much resembles that 

 of the common fowl, and is composed of similar elements. 



The glosso-hyal element is entirely cartilaginous in the Penguins. It is triangular in 

 form, and is prolonged posteriorly into two processes which represent the cerato-hyals, and 

 lie on either side of the first basi-branchial bone. 



The first or anterior basi-branchial element is completely ossified, and is prolonged 

 anteriorly into a pointed process which articulates with the glosso-hyal element. The 

 posterior extremity of the anterior basi-branchial is immovably connected with the 

 anterior extremity of the second basi-branchial element which in the Penguins presents 

 the form of an elongated, pointed, cartilaginous style, and occupies the interval between 

 the thyro-hyoid muscles of opposite sides. The anterior basi-branchial bone is expanded 

 posteriorly, and is furnished with two lateral facets which articulate wdth the proximal 

 extremities of the cerato-branchial elements. 



The latter are ossified throughout. They are long slender bones, which diminish in 

 thickness from their anterior to their posterior extremities. 



The epibranchials in the Penguins are strongly curved to adapt them to the posterior 

 surface of the skull. They diminish in thickness from their anterior to their posterior 

 extremities. They are ossified in the greater part of their extent, but, close to their 



In describing tiie separate elements of the hyoid bone, I have adopted the terminology used by Professor W. Kitchen 

 Parker in his work on the " Morphology of the Skull." 



