POKCELLIDIUM. 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 Glaus. 



4. POECBLLIDICJM SUBEOTUNDUM, Norman. PL LXXI, 



I. 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 

 cephalo thorax. Last thoracic segment (fig. 3 a) 

 laciniated at the angles; fifth pair of feet (6) triangular, 

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

 lamellae 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 -^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 



