ON TRILOBITES. 119 



Fam. 20. Cheiruridœ. —'Plam-.v with liiised band. Eyes finely facetted. Pygidium horned, spinose 

 or digitated. Typ. gen. : C7At7>Mn/s, Up. Cam., Dev. ; Deiophon, Vyi. SU.; Sj^hœrexochus, HU.; 

 Staurccephalus, Sii. ; Placoparut, Lr. Sil. 



Note. — The families of thi.s section are more or less closely connected by the peculiar course of 

 the facial t-iitures, alike in all, and by their typically eleven body-segments. The Bncrinuridaj and 

 Chciruridœ, are connected by their " bourreletted " pleuraj ; and this same condition — as well as their 

 spino.•^c character generally — connects the Chcirurida^ with the Acidaspidœ of the next section. 



§ 2. Armati. — Essentially broad-headed, spinose forms, with pointed or spiny pleura^, and small to 

 very small (commonly spinclicaring or digitated) pj'gidium. Body-scgmoiits 9 to 20. 



Fam. 21. Acidaspidœ. — Head, pleura) and pygidium, all spine-bearing. Body-segments 9 to 10. 

 PleurtB with " bourrelet." Typ. gen. : Acidaspes, Sil., Dev. 



Fam 22. P«rarfo.x((/(F.— Head-shield very large and broad, with horned angles and largo, anteriorly 

 expanded glabella. Body-segments 12 to 20; pleurœ, furrowed, terminating in spines; pygi- 

 dium very small. Typ. gen.; Paradoxides, Cam. ; HydrocepJmlus, Cam.: Teleplms (J) lii: SU. 



§ 3. Globosi.— Glabella large and prominent, oval, or globular, and unfurrowed. Thorax short, 

 with 5 to 6 segments. 



Fam. 23. Trinucleidce. — Head-shield very large, terminating in horns, and surrounded by a broad, 

 perforated border. Eyes commonly absent. Typ. gen.: Trinucleus,lir. S\\. ; DwmWe, Lr. Sil. ; 

 Microdiscus (?), Cam. 



Fam. 24. Ampyxida:— Head-shield without perforated border. Glabella extended anteriorly into a 

 strong spine. Eyes absent. Typ. gen. : Ampyx, Si\. ; Endymimia (J),^]). Cam. 



Fam 25. jEglinidœ.—GlaheUsi very large and globular, extended anteriorly, in some species, into a 

 stout spine. Byes abnormally developed. Typ. gen.: ^ÏJgUna,liv. Sil. 



Note.— This latter family forms a connecting link between the Globosi and the Oculosi. It 

 should, perhaps, be placed under the last-named section ; but it would appear to bo very closely allied 

 to the Ampyxidœ (notwithstanding the absence of eyes in that family) by its 5-6 body-segments, its 

 triangular pygidium, and its enormously developed glabella, which in some of its forms (e.g., uE. 

 armata, Barr.), extends forward into a distinct point or spine, much as in Ampyx. Whilst Barj-ande 

 makes ^Eglina the type of a distinct family, Zittel places it under the Asaphida". 



§ 4. OcuLOSi. — Eyes enormously developed. Head-shield with horned angles. Pygidium very 

 small, with 2-3 rings in its axis. 



Fam. 26. 5(//je??u7;((te.— Body- segments 5 in number. Typ. gen. : Bohemilla, Lr. Sil. 



Fam. 27. i?emo/)Zewnc/(F.— Body-segments 11 to 13 in number. Typ. gen. : Remopleurides, In: Si\., 

 Caphyra, Lr. Sil. 



