BY WILLIAM A. HASWELL. 
1715 
In Trygon pastinaca the hyoid arch {which, as in ZJrolophus, is 
exactly like the branchial arches), articulates partly with the 
proximal end of the hyomandibular,* but has also a separate 
articulation with the side-wall of the skull just behind the 
articular surface for the latter cartilage. Behind this again and 
close to it is a small separate articular surface for the first 
branchial arch. The succeeding branchial arches are all connected 
with the anterior vertebral plate. In Urolophus testaceus the 
articulations between the branchial arches and the anterior verte- 
bral plate are the same as in Trygon ; but the hyoid articulates 
wholly with the hyomandibular near its proximal end, and has 
no direct connection with the skull. In both species the copularia 
of the hyoid are narrow calcified cartilages, which are dii’ected 
from the ventral mesial forwards and slightly inwards ; at their 
anterior ends these are connected together by a slender bar which 
in Urolophus consists of a single cartilage, while in the specimen 
of Trygon pastinaca examined there are three separate pieces; 
this rod represents the hyoid copula. In Urolophus there is a 
small mesial cartilage between the middle of this hyoid copula 
and the anterior end of the basi-branchial plate ; this may repre- 
sent a separate copula belonging to the first branchial arch ; f it 
was not found in Trygon. In both species the ventral ends of the 
ventral mesials of the hyoid and of the first branchial arch are 
completely coalescent. In Trygon the most dorsal and most ventral 
of the branchial rays on each arch are broadened out into thin 
lamellae, which extend over a number of the others ; those seem 
to be the representatives of the external branchial arches found 
in the 8elachoidei. 
In the anatomy of the soft parts the following are the most 
important points to be obseiwed. The liver in both these genera is 
* On p. 102 of the paper referred to ‘hyoid’ ha.s been inadvertently 
printed for ‘ hyomandibular ’ in the second line from the top of the page. 
t A simular rudimentary copula occurs in a corresponding position in 
Spinax and Cestracion (Gegenbaur, “ Das Kopfskelet der Selachier,” p. 141, 
Taf. xviii. 6g. 6, and Taf. xix. fig. .3.) 
