15 TRINUCLEUS LATUS (Portk.), shewing antennary pores; from schists of Tyrone. 



16 TRETASPIS FIMBRIATUS (Murch. sp.) Entire specimen, natural size, from black shale of Pen 



Cerrig, Builth. 

 16a Ditto, magnified three diameters. 



17 ILL.^NUS LATUS (M'^Coy). Head natural size, from the limestone, Wrae Quarry, Upper Tweed. 



17 a Profile of ditto. 



18 ISOTELUS (Basilicus) LATICOSTATUS (Green sp.) Small, nearly perfect specimen from the 



schists of Rhiwlas. 



18 a A very large pygidium, natural size, from the schists of Maen Goran, Llangollen. 



19 DYSPLANUS CENTR0TUS2 (Dal.) Entire specimen, natural size, Llanwddyn. 



19 a Head, natm-al size, of a rolled-up specimen ; same locality. 



20 HOMALONOTUS RUDIS (Salt). Pygidium from the schists of Capel Gannon. 



20 a Portion of much larger ditto, same locality. 



21 Head of EURYPTERUS CEPHALASPIS (Salt). Upper Ludlow, Benson Knot. 



