NATURAL SCIENCES OF PHILADELPHIA. 183 



longer than the rest of the skull, very stout, in particular extremely 

 broad and obtuse. The nasal opening is correspondingly short. 

 The upper prong of the nasal bone is partly or wholly free from 

 the premaxillary. (Fig. 2.) The palatines are imperfectly anchy- 

 losed with the maxillae. The zygomata are extremely curved, 

 looping downward from the maxillo-jugal suture. The mandible 

 is abruptly deepened at its middle into a broad plate, and shows 

 no vacuity between the symphyseal and following elements. The 

 angle of the mandible lies in front of the mastoid plane. The 

 smooth interorbital space is narrow on top of the skull, since the 

 glandular depressions reach the anteorbital prominences. The 

 temporal fossae are very shallow, widely apart, and merely sepa- 

 rated from the depression between themselves and the cerebellar 

 protuberance by a slight bony ridge. The greatest width of the 

 skull is nearly half its length. 



C. Spheniscus demersus shows a third modification. (Figs. 3, 4.) 

 The rostrum is longer or no shorter than the rest of the skull, 

 very stout, in particular extremely deep, with the apex hooked 

 above, truncate below. The nasal opening is correspondingly 

 short. The upper prong of the nasal bone is almost completely 

 anchylosed with the premaxillary. The palatines are extensively 

 anchylosed with the maxillae. The zygomata are curved but 

 slightly downward. The mandible is deepened very slightly and 

 gradually, and shows no vacuity between the symphyseal and 

 succeeding elements. The angle of the mandible is below, if not 

 behind the mastoid plane. The smooth interorbital space on top 

 is narrow or reduced to a ridge. The temporal fossae are ex- 

 tremely deep, meet each other on the median line on top of the skull, 

 and are completely isolated from the depressions on either side of 

 the cerebellar protuberance by a strong flange-like plate of bone. 

 The greatest width of the skull is about two-fifths of its length. 



It will be observed that each of these t}-pes has its own pecu- 

 liarities. Thus A stands alone in characters of the rostrum; C is 

 isolated in the singularity of its temporal fossae ; B is peculiar in 

 the dip of the jugal and depth of mandible ; and the other charac- 

 ters vary in intensity of expression with each one. But there are 

 in each case other characters that are shared with one other, but 

 not with both the others ; and it is these combinations that render 

 the three distinct. I propose to establish genera upon them. 



