BY JAS. P. HILL. 
207 
the point of articulation of the propterygium with the shoulder 
girdle. The entire anterior portion of the left fin, supported by 
the propterygium and its rays, is thus entirely free from the body. 
On both sides, and especially on the left, the propterygia are 
directed markedly outwards. 
The only parallel for this condition among living Elasmo- 
branchs appears to be found in the Angel-fish {Rhina squatina). 
In that form, as is well known, the anterior ends of the expanded 
pectoral fins extend forward as two short horns supported by the 
propterygia, and entirely free from the body wall. On the left 
side of our specimen, except for the greater forward extension of 
the fin, the condition in Rhina is essentially realised. 
In the abnormal Thornback described by Dr. Traquair the 
anterior extremities of the pectoral fins projected as two short 
processes, one on either side of the snout. I have found a similar 
condition in one of a series of twelve young taken from a single 
female Ilypnos subnigrum. In this specimen, which measured 
6*1 cm. in length, the anterior ends of the pectoral fins projected 
as two blunt horns, one on the outer side of the anterior portion 
of each electric organ. 
Similar cases of the non-adherence of the anterior extremities 
of the pectoral fins to the head have been recorded by Yarrell* for 
Raia clavata, by Dayl for R. clavata and R. batis, and by 
Bureau | for R. asterias. All these cases are of the same nature, 
and of all recorded instances of this abnormality that of the 
Trygonorhina herein described is perhaps the most marked. The 
meaning of this variation, to which some slight importance may 
be attached from its occurrence in three distinct Batoid genera, 
is not far to seek. Prof. Howes, in his paper§ on the fin-skeleton 
* Yarrell. British Fishes, ed. by Richardson, 1859, Vol. ii. p. 585 and 
p. 384. 
t Day. British Fishes, Vol. ii. p. 345, PI. clxxi. fig. 2, and p. 337. 
% Bureau. Bull. Soc. Zool. France, 1889, xiv. p. 313, and fig. (References 
from Bateson. Materials for the Study of Variation, p. 540.) 
§ Observations on the Pectoral Fin-skeleton of Batoid Fishes. P.Z.S. 
1890, p. 680. 
