1714 JOTTINGS FROM THE UNIVERSITY BIOLOGICAL LABORATORY, 
note on the skeleton of a species of Urolophm, which, so far as I 
had examined it at that time, seemed to agree in almost every 
particular with that of Trygon pastinaca. A more careful study of 
the anatomy of the latter species and of the common Urolophufi 
testaceus, has, however, shown me that there are some important 
points of dilference which I previously overlooked. 
The agreement in the form of the anterior vertebral plate with 
its several ridges, processes and articular sui’faces is very close.* 
In both species the vertebrae of the posterior precaudal region 
undergo a varying amount of coalescence. In Urolophus a con- 
tinuous strip of calcified cartilage runs on either side of the centra 
throughout this part of the spinal column and renders the whole 
very rigid. In the skull both have much more prominent post- 
orbital processes than are generally to be found in the Rays ; and 
both have the pre-frontal foramen very wide and coalescent behind 
with the supra-cranial fontanelle ; in Urolophus the latter is much 
narrower than in Trygon. Both have a strong bridge of cartilage 
protecting the facial nerve where it emerges from the cranium. 
The absence of a distinct rostrum is characteristic of the family, but 
both have a ciu’ious cartilage situated between the nasal openings 
at the anterior end of the skull. This is divided behind into two 
slender crescents, each of which forms the inner margin of the 
corresponding nasal opening.! Trygon pastinaca has also a pair of 
singular little slender cartilaginous processes projecting almost 
directly forwards from the anterior border of the skull. The nasal 
cartilages are of similar general shape in the two species. In 
Urolophus there is a broad and very thin lamina of cartilage 
(upper labial) supporting the naso-frontal lobe ; and this is divided 
up behind into a fringe of very delicate filaments one of which 
supports each of the delicate filaments with which the lobe 
is beset behind. Whether this cartilage is present or absent in 
Trygon I am uncertain. 
* In the paper above referred to a paragraph on p. 104, which refers to the 
spinal column and ribs of Hypnos has been misplaced, so that it appears to 
form a part of the account of Urolophus sp. 
+ In the specimen of Trygon pastinaca previously examined these were 
not observed. 
