PORCELLIDIUM. 169 
other form to which that character would apply. The 
generic term Thyone, however, having been previously 
in use to designate a genus of Echinodermata, must give 
place to the name proposed by Claus. 
4, PORCELLIDIUM suBRoTUNDUM, Norman. Pl. LXXI, 
fies. 1—3. 
Porcellidium subrotundum, Norman. Brit. Assoc. Report, p. 297 
(1868). 
Body short, subcircular, nearly as broad as long, sub- 
truncate in front, broadly rounded behind; anterior 
antennee 6-jointed, short, not reaching the sides of the 
cephalothorax. Last thoracic segment (fig. 3 a) 
laciniated at the angles; fifth pair of feet (b) triangular, 
with a few spine-like setee on the distal margin ; caudal 
lamelle broad and square; three setz on the outer 
and one on the inner distal angle. Colour pale 
yellowish green, more or less tinged with pale purple 
or violet ; integument not pitted. Length 'srd of an 
inch (‘77 mm.). 
Not so common as either of the two foregoing 
species, but occurring in similar positions. Hiullswick, 
Shetland (fev. A. M. Norman) ; Clifden and Birtirbuy 
Bays, and Portincross (Firth of Clyde). 
I retain this species more out of deference to 
Mr. Norman’s practised judgment in the matter of 
‘specific distinctions, than from any conviction of my 
own as to its validity. Indeed I am very much disposed 
to suspect that it may be found to be a form of the 
