REV. A. MERLE NORMAN, M.A., ON THE CRUSTACEA. 269 
It will be observed, first, that the proportionate depth of the 
rostrum becomes greater as the animal approaches maturity, and 
secondly, that although the number of teeth on the upper side of 
the rostrum increases with age, no such increase takes place with 
regard to those of the lower surface. 
The tip of the rostrum, the short interior antenne, the scale 
of the exterior antenne, and the extremity of the pedipalps are 
all of nearly equal length. The first feet are stout, of moderate 
length, a little exceeding half the length of the second pair. The 
wrist of the second feet is divided into seven articulations. 
The posterior margin of the third abdominal segment is but 
little produced, so slightly indeed that the central lobe would 
scarcely be noticed unless it was especially looked for. 
The telson (Pl. XII., fig. 7) is armed with three (rarely four) 
pair of spines on its surface, and ends in six spines, the two 
central and two outer of which are short and blunt, the two inter- 
mediate considerably longer. 
Hf. securifrons approaches more nearly to H. spinus (Sowerby) 
than to any other of our recognised species. The latter may be 
more especially distinguished from the former; jirst, in having 
the dentated keel continued to the hinder margin of the carapace ; 
secondly, in the four posterior teeth being of considerably 
greater size than the teeth anterior of them; ‘thirdly, in the 
fact that the teeth in the upper margin of the rostrum are 
themselves furnished with secondary teeth ; and jourthly, in 
having the dorsal centre of the third abdomenal segment pro- 
duced backwards into a conspicuous tooth-like process. 
It is not improbable that some of the Hippolytes which have 
been considered by our collectors to be H. spinus, more properly 
belong to this species. I have figured Pl. XII, fig. 8, the rostrum 
of H. spinus, dredged by me at Oban, for comparison with the 
rostra of the present species. 
The examination of the specimens of H. securifrons, from this 
coast, has proved the extent of variation in this species to be 
so great that possibly it may hereafter prove to be identical not 
only with H. turgida of Kroyer, but also with H. Phippsii of the 
same author, 
