some British Fossil Crustacea. 399 



largely faceted ; facial suture cutting the lateral cephalic mar- 

 gin in front of the angles ; eleven thoracic segments. 



Subgen. 1. Phacops (Em.). Pygidium with eight to twelve 



joints in the axis ; hypostome simple. 

 Subgen. 2. Odontochile* (H. & C). Pygidium with twelve 



to twenty-two joints in axis ; hypostome dentated. 

 Subgen. ? 3. Chasmops (M'Coy). Eyes small, "hiant;" 



middle pair of lateral glabellar lobes obsolete. 

 Subgen. 4. Portlockia (M'Coy). Two anterior pair of lateral 



glabellar lobes obsolete ; lateral cephalic angles rounded. 



2. Calymene (in a wider sense than Brongniart). Lateral ce- 

 phalic angles not prolonged, exactly bisected by the facial 

 suture ; eyes small, " hiant ;" glabella narrower in front than 

 at base ; thirteen thoracic segments. 



Subgen. 1. Calymene (Br.). Axis of body strongly defined 

 from the lateral lobes ; three segmental furrows to each 

 side of glabella. 



Subgen. 2. Homalonotus (Konig). Axis not defined from 

 lateral lobes ; no segmental furrows to glabella. 



3. Trimerocephalus (M'Coyt). General character of Port- 

 lockia, but without eyes or facial sutures. 



4. Asaphus (in a wider sense than Brong.). Cephalic and cau- 

 dal shields nearly equal ; external cornea thick, smooth ; facial 

 suture cuts the posterior margin within the angles; eight 

 thoracic segments. 



Subgen. 1. Asaphus (as restricted to the type of A, corni- 

 gerus, not British) =Hemicrypturus (Gr.). 



Subgen. 2. Isotelus (DeKay). 



Subgen. 3. Basilicus (Salt.). General character of Isotelus, 

 but with many simple segmental furrows to pygidium. 



5. Ill^nus (Dal.). Head and tail nearly alike, axal furrows 

 only indenting their margins ; facial suture cutting the poste- 

 rior margin ; pleurse with long, narrow, obscure facets and no 

 pleural grooves. 



Subgen. 1. Illcmus (Dal.). Ten thoracic segments, lateral 



cephalic angles rounded. 

 Subgen. 2. Bumastus (Murch.). Resembling Illamus, but 



the thorax not trilobed. 

 Subgen. 3. Dysplanus (Burm.). Like Illcenus, but cephalic 



angles prolonged and only nine thoracic segments. 



6. Forbesta (M'Coy). Glabella distinct; facial suture cutting 

 the middle of posterior margin ; pygidium with articulated axis 



* Dalmannia of Emmerich, not of Robineau-Desvoidy. 

 f For characters see below. 



