NATURAL SCIENCES OF PHILADELPHIA. 23 



PHOC^NA Cuvier. 



PnOCiKNA VOMERINA Gill. 



Proc. Acad. Nat. Sci. Pliila. 1865, 178. 



This well defined species is the Bay Porpoise of the present essay. 



I5ELUGA Lacep. 



Capt. Scammon has not p;iven any definite characters by which the species 

 of thig genus occurring in Northern Pacific waters may be distinguished. I 

 take, however, the present opportunity to make public descriptions of two spe- 

 cies of this genus from the Arctic Seas. They have been already described by 

 me, but rather briefly. First is the Beluga rhinodon Cope, Proc. Ac. Nat. Sci. 

 Phil., 18G.5, 278. 



The cranium is peculiar for the breadth and shortness of the muzzle and its 

 sudden contraction ; the fewness of the teeth ; the large extent of the vomer 

 ])roduced behind the palatines : and the long proportion of the maxillaries in 

 front of •tlije nares uncovered by the intermaxillaries. 



The length of the muzzle to the notch equals the distance from the latter 

 point to- the crest at the inner extremity of the os parietale ; its breadth at the 

 same point is about three-fourths the length and less than the width of the 

 cranium at the orbits. The prenarial exposed portion of the maxillaries is 

 parallelogrammic, the length about two and a half times the width, and ex- 

 tends very nearly to a line connecting the fundus of the maxillary notches. 

 The maxillaries present ho other carina than a short one on each side the 

 o. 0. nasalia. 



Tl>e premaxillaries terminate opposite the posterior extremitj- of the vomer, 

 and are deeply grooved for the outlines of the " triangle," which terminates 

 with the basal third of the muzzle. They are one-third wider than the max- 

 illaries (from a vertical view) at the middle of the muzzle, where the contrac- 

 tion is strongest, and form with them an arch of neaily 180° width at the in- 

 ternal fpiamen three-fifths width from outer margin to notch of maxillary. 



The median portion of the palatines is narrowed, and with an inner angle 

 just prevent the contact of the maxillaries and vomer. The outer wing is also 

 narrow, and impressed externally with a broad groove ; it extends as far as 

 opposite" the squamosal process. The latter bone is not in contact with the 

 postorbital process, and presents a large internal lamina, which overlaps 

 without touching the alisphenoid. Posterior upper vomer plate with the deep 

 corner emarginations seen in Phocaena. 



Posterior^'emporal crest not developed; exoccipitals flat, slightly concave 

 externalljiiytj. Supraoccipital with two large fontanelles and above the foramen 

 two impressions for insertion of muscles. Line to the weak spine straight, 

 Crest not diiveloped ; frontal band broad, flat ; knob above nasals slight. 



In. Lin. 



Length frolo end of muzzle to concavity of occ. condyle 16 0-8 



" " " occipital spine 14 8-8 



» If" " nares 9 10 



'^-' " " maxillary notch 7 7-5 



', of temporal fossa 5 1 



" " of orbit 1 11-4 



"•Vof ramus mandibuli 12 



" ^«f gonys 1 9-5 



Breadth at distal 2-5ths of muzzle 2 5 



" at notch 5 6 



" at orbits 8 11-4 



" at frontal margins 8 68 



*• of foramen magnum 2 2-5 



V* of paroccipital alifi 7 2-8 



^> " of external nares 2 2-2 



Teeth | 



1869.] 



