SUBCLASS I 



TEILOBITA ' 



711 



Eodiscus Matthew (Microdiscus Salter non Emmons) (Fig. 1357, B). Glabella sliort, 

 occipital ring spined. Lower and Middle Cambrian ; Europe and North America. 



Goniodüc'us Eaymond. Glabella long, occipital ring obtusely pointed. Type, 

 Microdiscus lobatus Hall. Lower Cambrian ; North America. 



Family 3. Shumardiidae Lake, ' 



Hypoparia similar to the Ägnostidae in size and in structure of the cephalon, hut 

 with small, strongly segmented pygidium, and six segments in the thorax. 



Shumardia Billings. Glabella prominent, expanding toward the fi-ont. Lower 

 Ordovician ; Europe and North America. 



Family 4. Harpedidae Corda. 



Hypoparia with very large head shield and small pygidium. Free cheeJcs ventral, 

 suture marginal. Thorax with numerous segments {seventeen to twenty-nine). Cephalon 

 loith hroad pitted hrim. Ordovician to Devonian. 



The broad hippocrepian pitted brim of the Harpedidae has its counterpart in 

 Cryptolithus and Dionide, although less well developed in those 

 genera. The head is also relatively longer and larger, both 

 features being decidedly larval. The functional visual spots or 

 ocelli, situated on the fixed cheeks, are found only in this 

 family and in Tretaspis and in the young of Cryptolithus. The 

 great number of thoi'acic segments is another primitive 

 character, and the cephalon is larger than the thorax and 

 pygidium. 



Harpes Goldfuss (Fig. 1357, C). Hypostoma somewhat 

 pentagonal, angular in outline. Silurian and Devonian ; 

 Europe and North America. 



Eoharpes Kaymond (Harpina Novak) (Fig. 1360). Hypostoma 

 oval in outline. Ordovician ; Europe and North America. 



Flu. 1360. 



Koharpes ungula (Stern- 

 berg). Ordovician ; 

 Bohemia. l/i (after Bar- 

 tande). 



Family 5. Trinucleidae Emmrich (Cryptolithidae Angelin). 



Hypoparia with large cephalon and small pygidium. Free 

 cheeks ventral, carrying the genal spines. Cephalon with a pitted, 

 brim. Thoracic segments few (ßve or six). Ordovician. 



Cryptolithus Green {Trinucleiis Murch. pars) (Figs. 1346, 1357, 

 D; 1361). Central portion of cephalon divided by the dorsal 

 furrows into three prominent portions. No ocelli in adult. 

 Ordovician ; Europe and North America. 



Trinucleus Murch. (restr.). Glabella obovate, with two pairs 



of weak glabellar furrows. Pits on brim set in deep radiating 



furrows ; no ocelli or eye-lines. Ordovician ; Europe and North 



America. Type T. fimhriatus Murch. 



Glabella spherical in front, conical behind, with two pairs of 



iye-lines present. Ordovician ; Europe and 



Fig. 1361. 

 Cryptolithus gohlfus.'^i 

 (Barr.). Ordovician (Etage 

 D) ; Wesela, Boliemia. 

 xVi. 



Tretaspis M'Coy. 

 strong glabellar furrows ; ocelli and 

 North America. 



Dionide Barrande. Similar to Cryptolithus, but with an irregularly pitted border 

 and a large pygidium. Ordovician ; Europe. 



