of the North Atlantic and of North-Western Europe. 707 



seta, last joint with two somewliat shorter terminal setse ; the second branch has 

 the first joint naked, much surpassing the length of the two remaining joints, 

 which are very short, and furnished with a terminal bunch of long setae. The 

 mandible fPl. lv., fig. 13) has the biting process divided into five teeth, palp two- 

 jointed, the first bulbously swollen on the inner margin, which bears four setae, 

 its outer margin furnished with a small bisetose laminar appendage ; the last 

 joint has three setae on its inner margin and four at the apex. First maxilla 

 (PI. Lxvii., fig. 3) composed of a short and broad setiferous lobe with a very 

 large four-jointed palp ; the maxillary lobe bears several plumose setae and a 

 papilla, from which spring two large and one small unguiform setae ; basal portion 

 of the palp very stout, its first joint much broader than long, and bearing on its 

 inner margin a fascicle of seven or eight plumose setae ; second joint about twice 

 as broad as long, giving attachment on its distal margin, internally to two 

 plumose setae, and externally to a large one-jointed laminar appendage, which 

 reaches as far as the extremity of the limb, has three setae near the middle of its 

 outer edge, and at its obliquely truncated apex nine very long and slender ciliated 

 setae ; tlie third joint of the palp is much less stout than the preceding, and has a 

 single stout plumose seta on its inner edge ; terminal joint short, obliquely 

 truncated at the apex, and bearing seven plumose setae, the innermost of which is 

 much longer than the rest. Second maxilla (PI. lv., figs. 14, 15) three- jointed, 

 two lower joints broad, the first being ciliated on its lower margin, which also 

 bears one small distal seta ; to its front margin is attached a semi-elliptic branchial 

 plate, edged with setae; second joint also having the lower margin finely ciliated, 

 on each margin towards the extremity a densely ciliated seta, and at the extremity 

 five densely ciliated but not long setae; last joint very narrow and small, nearly 

 thrice as long as broad, but only sufficiently wide to support the one short densely 

 ciliated and somewhat unguiform seta, in which the limb ends. Caudal laminae 

 (PI. LV., fig. 16) deeply incised for the reception of each of the eight somewhat 

 spiniform ungues, which are ciliated on their inner margins and not conspicuously 

 dilated at their base ; the ungues progressively increase in length from the first to 

 the last, and the intercurrent projections of the caudal laminae are broadly 

 triangular in form, with sub-truncate apices, except the last, which is chisel- 

 shaped, sharp at the apex, and twice notched on its anterior margin. Length of 

 female "GS mm. ; male unknown. 



Habitat. — Besides the localities enumerated in the " Monograph of recent 

 British Ostracoda," we have records of the occurrence of P. orbicularis in the 

 following places: — LochFyne; Cumbrae, 16 fathoms ; Rothesay and Kilchattan 

 Bays; Clew and Birtirbuy Bays; Lough S willy ; off Valentia, 112 fathoms; New 

 Grimsby Harbour, Scilly Islands, and at several points off the coasts of Durham 

 and North Yorkshire. 



