NATURAL SCIENCES OP PHILADELPHIA. 295 



basal one-fourth, one third breadth of combined premaxillaries, not recurved 

 on the margin. Antero-exteiior ridge of nasals prominent, enclosing two pita 

 behind margin of vomer ; median portion of f rentals separating nasals well from 

 supraocoipital, and the same from each other by an anterior process ; with an 

 anterior process of supraoccipital forming a prominent knoh. Supraoccipital 

 crest remarkahly strong and directed nearly horizontally forwards. Pterygoids 

 in contact on the median line, posterior margins widely divergent ; inferior 

 angles separated, much rounded, median depression considerable. Common 

 suture of palatines considerable, nearly equal gonys. Maxillaries closely in 

 contact on the palate, not exhibiting vomer or premaxillaiies, except a little 

 of the latter on the distal inch. Corouoid process of mandible everted : ramus 

 on distal half thickened internally, so that the dental series converge far less 

 on the posterior half its length than on the anterior. Occiput transverse, little 

 convexity between the posterior ridges of the temporal fossae. Latter large, 

 subrhomboid in outline. No portion of maxillaries visible between prenareal 

 swellings ; these elevations descend gradually anteriorly and are steep later- 

 ally, not grooved. Longest (right) prolongation of premaxillary not attaining 

 nasal hone. 



The remaining and more prominent features of this species are apparent from 

 the following measurements : 



Length from end muzzle to convexity of occipital condyle 35-25 



" " " notch 7-6 



Depth of cranial chamber 4 - 9 



Length of ramus mandibuli 11.75 



" gonys 1 -25 



Width at temporal fossa? 7 



" orbits 6-5 



" notch 3-79 



" middle of muzzle 2*5 



" of prenareal elevations 279 



The shelving form of the supraorbital plates of this species suggests a re- 

 lationship to the Delphinus (Tursio) eu tropia, Gray, but it is evident that 

 the S. amblodon differs entirely from any species of Delphinus hitherto 

 known. 



The habitat of this species is uncertain. It was taken off the ship Vincennes, 

 of the U. S. Exploring Expedition. On inquiry of Dr. Charles Pickering, 

 naturalist on board of that vessel, he has no record or recollection of the cap- 

 ture of such a species ; it was therefore probably procured while he was absent 

 from the ship from Cape Horn to Lima, or afterwards during his stay on laud 

 in Australia and New Zealand. 



Delphinus longidens. 



Of the type of D. (Tursio) obscurus Gray, but with considerably longer 

 muzzle and much longer prenareal triangle, the rugose surface of which ex- 

 tends to the end of the basal third of the length of the muzzle. Muzzle from 

 notch just twice the length of cranial chamber, shorter than mandible, flat above 

 on the basal two-thirds, the premaxillaiies continuous with maxillaries, not 

 bounding the triangle in front by a ridge. Sides of muzzle quite steep near 

 tip. Prenareal portion of triangle full plane. Premaxillaiies not visible on 

 palatine surface till near tip; pterygoids not in contact, prominent ridge. Teeth 

 slender, acute, spreading, four and an interspace iu an inch, so, anteriorly 



not separated by alveolar partitions ; occiput flat, rounded in profile ; nasal 

 bones subtransverse, very near the moderate supraoccipital crest. 



in. 



Length of cranial chamber 4 



v " cranium, total , 15-25 



" mu/zle to notch 8-25 



" mandible 1225 



1866] 



