542 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Juiie 13, 



The foramen magnum is subcircular, a little wider across than 

 vertically ; measuring 1 inch across. The condyles are 4 lines apart 

 at their lower ends, with the articular surface divided into two tri- 

 angular facets, meeting at rather more than a right angle, along an 

 oblique ridge, where the surfaces are continuous. In Manatus the 

 occipital foramen is broader across, and the condyles are more uni- 

 formly convex, and are separated from each other by a broader basi- 

 occipital, which contributes a portion to the lower end of each con- 

 dyle. The occipital surface of the fossil cranium is less bent from 

 below upwards and forwards than in the Sirenia ; it has not the 

 median vertical longitudinal ridge which is seen in Manatus ; and 

 the super occipital ridge appears, from the small portion preserved, 

 to have been reflected back, so as to overhang the occipital wall, more 

 than in any recent Manatee. 



The exposed facial part of the skull includes a great part of the 

 right orbit (fig. 2, o\ the external nostril {n), the premaxillaries (22, 

 wanting their anterior ends), and the corresponding parts of the 

 rami, with the symphysis of the lower jaw. 



The orbit is round, \\ inch in diameter, with the lower border 

 continued outwards, not so far as in the Manatee, but further than 

 in the Tapir, or in other land mammals of the same size as the fossil. 

 The back part of the orbit is broken way, and the upper and fore 

 parts are mutilated. I perceive no trace of lacrymal pit or foramen 

 at or near the inner border of the orbit. 



Part of the frontal bone and the nasal bones are broken away ; but 

 the anterior boundary of the nasal opening is entire : the plane of 

 the opening is almost horizontal : the sides converge and terminate 

 in a point, 2 inches in advance of the fore part of the orbit. I 

 cannot satisfactorily determine the sutures of the premaxillaries ; 

 but appearances are most in favour of their extending backwards 

 along the sides of the nostril to the orbit : in front of the nostril 

 the premaxillaries unite to form a massive convex muzzle, which 

 curves gently forwards and downwards, 2\ inches in advance of the 

 nostril ; and perhaps a little more when entire. 



The round orbit, turned upwards by the produced floor, the almost 

 horizontal nostril, and massive premaxillaries are the chief features 

 of resemblance which this skull presents to that of the Sirenia, and 

 more especially of the Manatees; and the same resemblance is kept up 

 by the long, compressed, and produced symphysis menti, fig. 4. The 

 rami of the lower jaw are thick and rounded below ; they meet at a 

 very acute angle. The mental foramina are large, and the emerging 

 canal deeply grooves the bone in advance of it, as in the Manatee ; 

 but the symphysis becomes more compressed than in any Manatee, 

 forming almost a ridge at its anterior half, where it slopes from the 

 alveolar border backwards at a very open angle with the horizontal 

 rami, resembling the prow of a wherry (whence the generic name here 

 proposed for the fossil *). The bone, wherever fractured, shows the 

 dense compact structure of that of the Manatee. The most essential 

 distinction from the Manatee is the presence of, at least, two functional 

 * Prorastomus, from Gr. Trpujpa, a boat's prow, and arofia, a mouth. 



