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 POBCELLIDIGTM SUBKOTUNDUM, Norman. PL LXXI, 



!. 13. 



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 

 antennae 6- jointed, short, not reaching the sides of the 

 cephalothorax. Last thoracic segment (fig. 3 a) 

 laciniated at the angles; fifth pair of feet (&) triangular, 

 with a few spine-like setae on the distal margin ; caudal 

 larnellse broad and square ; three setae 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 - 3 ^-rd of an 

 inch ('77 mm.). 



Not so common as either of the two foregoing 

 species, but occurring in similar positions. Hillswick, 

 Shetland (Rev. 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 



