BY WILLIAM A. HASWELL, M.A., B.SC. 101 



of a somewhat complicated articulation. Each lateral lamella, 

 formed apparently as above noted by the transverse processes, 

 developes just below the part where the mesial bar arises 

 from it, a thick, laterally projecting process with a truncate 

 terminal face ; above and a little behind this is a wide 

 aperture in the root of the horizontal lamella into which the dorsal 

 end of the pectoral arch fits, while the truncate lateral process 

 articulates with a concave oval surface on the inner border of the 

 arch at some little distance below. There is a considerable 

 resemblance between this arrangement and that already described 

 as occuring in Trygonorhina, except that in the latter there is no 

 connection between the horizontal bar and the lateral laminae, 

 and the articulation with the pectoral arch is effected entirely 

 through the former, which is a development from the spinous ridge. 



Another peculiarity which the anterior vertebral plate of 

 Trygon presents is the presence of a series of articular facets for 

 the branchial arches. The chief of these articular surfaces is 

 that for the fifth branchial arch ; this is situated on a little 

 angular projection on the lateral border of the vertebral plate, 

 close to the front portion of the lateral lamina. In front of and 

 a little internal to this on the ventral surface of the plate is a pair 

 of short triangular ridges ; these articulate or are synchondrosecl 

 with the basal plates of the fourth branchial arch. In front of 

 and a little external to those, near the lateral borders of the plate, 

 is a pair of small elevations which articulate with the third 

 branchial arch. There are no ribs attached to any part of the 

 spinal column. 



Skull and Visceral Arches. (Plate II., fig. 12.) 



In the skull the plane of the foramen magnum is very nearly 

 vertical. The occipital condyles lie a little behind, on projecting 

 processes. The orifice for the vagus is close to the foramen 

 magnum. The elevations for the anterior and posterior semi 

 circular canals are tolei'ably well marked. The orifices of the 

 auditory organs are situated far apart, and are not connected by 



