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



secondary cusps not present in upper post-canines except occasionally in 4th and 5th ; 

 in lower post-canines secondary cusps not unfrequently present. Teeth single-fanged 

 except the last lower and last two upper post-canines. 1 



Halichcerus grypus (Fabricius). Grey Seal. North Atlantic Ocean. 



Phoca grypus, Fabr., Skr. Nat. Selsk., i. p. 167, pi. xiii. fig. 4, 1790. 

 Halichaerus griseus, Nilsson, Skand. Faun., i. p. 377, 1820. 

 Phoca gryphus, Fischer, Syn. Manila., p. 239, 1829. 



The only species. 2 



Interorbital constriction of frontal somewhat swollen about the middle. Occipital 

 and sagittal crests present and not unfrequently a squamous ridge. Nasals wider than 

 in Phoca and not ankylosed together. Premaxilla not expanding at its upper end and 

 with only a limited articulation to outer border of nasal, not reaching its tip ; the two 

 premaxilke curve outwards from side of nasal, so that the widest part of anterior nares 

 is in the upper third and the opening generally is very capacious. Z}-gomatic arches 

 bulging, widest part of arch in the middle and much wider than the widest part of the 

 cranium. Hard palate with rounded arch at posterior border, the crown of the arch 

 considerably in front of both the hamulars and the malo-zygomatic joints ; posterior 

 border of vomer visible in concavity of arch, but soon joining vomerine crest of 

 palate. Horizontal part of premaxilla thicker than in Phoca and with distinct tubercle. 

 Tympanic bulla swollen, generally smooth, but with a ridge in outer half, which is 

 prolonged into thick wall of external auditory meatus. Foramen lacerum posterius 

 moderate. Basi-occipital usually not perforated mesially. Par-occipital short. Mandible 

 with a stunted, vertically elongated, subcondyloid process, scarcely inverted and quite 

 distinct from the tubercle at the angle ; lower border of body thickened and scarcely 

 inverted ; masseteric fossa very deep, coronoid broadly triangular. 



1 Nehring (Sitzb. der Gesellsch. naturf. Freunde zu Berlin, October 17, 1882) gives an account of Halichamis grypus, 

 and refers to variations in the skull due to age and sex as well as individual modifications. He points out that the 

 roots may vary in number in the hinder post-canine teeth, and that the accessory cusps are variable in the lower post- 

 canines. He also states both from his own observations and those of Professor Gerstaecker that an accessory 6th upper 

 molar not unfreijuently occurs. Gerstaecker has seen it eight times in thirty-four crania, five times on one side only, 

 thrice on both sides. I may also refer to the skull of a young Halichoerus grypus which I described in the Journ. of Anat. 

 and Phys., vol. vii. p. 273, 1873, in which no teeth were developed except the canines. 



2 This Seal is often regarded, in so far as its distribution in Scotland is concerned, as restricted to the west coast, but, in 

 addition to specimens from that side of the island, I have placed crania in the Anatomical Museum of the University 

 from animals killed at the mouth of the Tay, off Montrose, at Golspie in Sutherlandshire, and from the Shetland 

 Islands. 



