Cope.] ^^^ [Aprils, 



the middle are as follows : vertical, 71 mm.; transverse, 47 mm. It is a 

 little larger than those I have seen hitherto, but agrees with them in every 

 respect. Plate vi. Fig. 6. 



Cetotherium megalophysum, sp. nov. 



This species is established on a cranium which is complete from the 

 condyles to near the anterior extremity of the nasal bones inclusive. The 

 apices of the zygomatic processes of the squamosal bones and the left 

 auricular bulla are wanting. The presence of the right bulla in the 

 specimen enables comparisons to be made with species in which this part 

 is preserved and where the cranium is wanting. The skull has lain in 

 the water for a considerable time, as numerous barnacles and oysters 

 have attached themselves to it. The matrix has been generally removed 

 from it by the action of the water. 



The cranium presents the characters of the genus in the close approxi- 

 mation of the temporal fossae on the middle line and the elongation of 

 the frontals anterior to this point. Portions of premaxillaries and max- 

 illaries remain at positions much posterior to that of the external nares. 

 The glenoid surface is separated by a sharp angle from the temporal fossa. 

 The sphenoid and presphenoid are keeled on the median line. The vomer 

 is visible between the palatines on the middle line below. 



The lateral occipital crests form with a line connecting the exoccipital 

 processes across the foramen magnum, an isosceles triangle with straight 

 sides, each of which is rather shorter than the base-line mentioned. The 

 apex of the supraoccipital is not elevated, and is well produced forwards, 

 so that the length of the cranium from the posterior border of the frontal 

 bone is one and one-half times as long as the depth of the cranium at the 

 same point. 



The tympanic bulla has the general form characteristic of species of 

 this genus, but presents specific characters of its own. The part anterior 

 to the posterior boundary of the external process is half as long again as 

 the length posterior to it. The two measurements are equal in the C hup- 

 schii, according to Van Beneden. The two ridges of the internal border 

 unite 19 mm. posterior to the anterior extremity, forming a single acute 

 angle. This character is not described by authors as occurring in any 

 other species of this genus. The anterior extremity is squarely truncate, 

 and is semicircular in outline, as the superior side is flat and the inferior 

 convex. In C. brialmoatii, according to Van Beneden, the bulla is not 

 truncate in front nor is there a single acute edge on the inner side in 

 front ; the portions of the bulla anterior and posterior to the internal pro- 

 cess are of equal transverse widtli ; in the 0. megalophysum the anterior 

 portion is considerably narrower than the posterior portion. In Mesoce- 

 tus agramii, according to Van Beneden, there is a single acute internal 

 ridge on the bulla, but it is much longer than in the Cetotherium megalo- 

 physum and the anterior extremity of the bulla is rounded and not trun- 

 cate in the former. The bulla in the species now described presents an 



