MUSEUM OF COMPARATIVE ZOOLOGY. 9 



a postparietal or epiotic process ; this process, with a pore (k) iu front 

 of it, recalls a similar arrangement on the skull of Rhina. The third (l), 

 pterotic, is formed by the backward extension of the edge of the cup 

 receiving the end of the hyomandibular. This pi'ocess is quite promi- 

 nent ; its height is more than half that of the skull, and the upper angle 

 is produced. The articular depression, extended by this process, meas- 

 ures about five eighths of an inch in length by one fourth of an inch in 

 height. The articulation permits the hyomandibular to lie against the 

 side of the skull, or to be turned sidewise at an angle of forty-five de- 

 grees. On the side of the skull appear the openings for the second to 

 the seventh pairs of nerves (2 to 7), the nostrils (c), and the orbito-nasal 

 canal (x). In the orbit the articular facet for the palatal or trabecular 

 process of the quadrato-pterygoid (tp) extends nearly to the top of the 

 skull, and is produced below the floor in a prominent ridge. Immedi- 

 ately in front of the deep cavity in which is found the opening for the 

 fifth pair of nerves (5) is the short style (os) connecting with the eye- 

 ball. In the section (Plate VII.) the opening for the optic nerve (2) is 

 shown to be farther forward and upward than in the Notidanidse ; the 

 olfactory lobe passes out but a short distance in front of it. Between 

 and below the openings for the fourth and fifth pairs there are carti- 

 laginous bridges (iv, r). The pituitary cavity (joy) is shallow, and 

 around the opening for the internal carotid the wall is thin. The 

 thread-like termination of the notochord lies close to the lower face 

 of the wall. Around it, in the parachordal region, the cartilage is hard 

 or granular. 



There are no spiracular cartilages (metapterygoids). 



TJie Jaws and Hyoid Cartilages. 



Plates VII. -IX. 



Labial cartilages at the angles of the mouth and along the jaws have 

 not been found. 



The suspensorium, hyomandibular (km), is about three inches long, 

 depressed, curved, and tapers in the hinder third of its length, where 

 applied to the pterygo-quadrate. Its thickness is about one half of its 

 width. The curvature is but moderate, certainly not more than that 

 of a circle with a diameter of six inches. The end articulating with 

 the ceratohyal is small. Anteriorly the articulating surface is oblique, 

 forming an angle of about forty -five degrees with the shaft ; posteriorly 

 the shaft has tapered to less than half its width. The inner (hinder) 

 edge is sharper, and bears nine branchial rays (br-?-). 



