AND MESOPLODON SOWERBYI. 777 



tooth on each side, is situated nearer the tip. But these differences also, I would 

 submit, are of specific and not of generic import. For, although modifications, 

 such as I have described, occur in the construction of the beak, in the form of 

 the lower jaw, and in the position of the mandibular teeth; the conformation of 

 the nasals, pre-maxillaries, and maxillae, in the region of the anterior nares, 

 presents but slight modifications in Soiverbyi, densirostris, Layardi, and euro- 

 pceus. Hence, I am disposed to consider that it is in the region of the anterior 

 nares, and in the bones surrounding these orifices, we are to look in the Ziphioid 

 group of whales for the characters which indicate generic resemblance or dis- 

 similarity, whilst the beak and lower jaw furnish us with the characters on 

 which specific relations may be based. 



For if we recur to the group of crania, which in the first part of this memoir 

 I have classed under the head of Ziphius cavirostris, we find that they all 

 possess, from the peculiar shape of the pre-maxillse, a wide and deeply excavated 

 pre-nasal fossa, at the bottom of which the anterior nares open, and that in all 

 the unsymmetrical, lobate nasals, with their shelving pent-house-like projection, 

 overhang the anterior nares. In the construction of the beak modifications 

 such as I have described occur in various of these crania, but in none can these 

 modifications, if they are to be regarded as anything more than mere individual 

 or sexual variations, be considered as marking more than specific differences. 



Again, all the crania which I have referred to in the historical sketch of 

 Sowerby's whale, agree with that animal in the absence of a pre-nasal fossa ; 

 for in these skulls the pre-maxillse ascend almost vertically, and with their 

 anterior surfaces so flattened, and the nasal bones so included between them, 

 that the anterior nares open directly, if I may so say, on the anterior plane of 

 the skull, and not at the bottom of a deep pre-nasal fossa. And although in the 

 construction of the beak, in the conformation of the lower jaw, and in the position 

 of the mandibular teeth, differences occur which may fairly be regarded as 

 specific, yet their common naso-premaxillary arrangements unite them, I believe, 

 into a single genus. 



Are we then to consider, as has been done by Professor Owen, that 

 Sowerby's whale and its allies belong, like the cavirostris of Cuvier, to the 

 genus Ziphius, and form distinct species of that genus, or are we to regard 

 them as forming a distinct genus, having various specific subdivisions ? The 

 value which I am disposed to attach to the conformation of the naso-premaxil- 

 lary region in the Ziphioid group of whales, as a basis for classification, leads me 

 to the conclusion that Sowerbyi, with its congeners, should be placed in a genus 

 distinct from cavirostris. Reserving them for the latter, the name of Ziphius, 

 which was originally applied to it by Cuvier, I shall adopt Gervais' name of 

 Mesoplodon as the generic designation for Soiverbyi and its allies. This genus 

 may be regarded as including the following species : — 



