264 W. HAROLD LEIGH-SHARPE 
the siphon tube is too narrow to admit of complete eversion. 
The muscle band is dorsolateral in position (figs. 6 and 10) on 
the outer side of the middle line. 
Attention has already been drawn to the circumstance that 
the claspers of the skate possess a minimum of skeletal support. 
On the other hand, they are provided with an excess of erectile 
tissue (to be figured for another species in an ensuing memoir). 
I have been present at Plymouth, at the trawling of a speci- 
men of Raia circularis, taken immediately after copulation, in 
which the claspers were swollen to four times their natural size, 
and appeared of a rose-pink hue due to a suffusion of blood. 
Fig. 12. Raia circularis, a single strand of striped muscle cells from the dor- 
sal muscle bundle of the siphon (Farrant’s medium, unstained). m., nodes; f., 
terminal cell functioning as a tendon. 
Such an erection is not needed in Scyllium and Acanthias, 
which are provided with dermal denticles and spurs, respec- 
tively, while Raia relies on this phenomenon and on a relatively 
larger rhipidion for fixative purposes during impregnation. 
Such are the elementary facts, several of them new, drawn 
from the four most common representatives of elasmobranchs 
found around British coasts. It is when we consider the prob- 
lems arising out of these, and compare these types with other 
less known and intermediate forms, that the subject grows more 
interesting. 
