PALEOZOIC TIME — CAMBRIAN. 



473 



7. Crustaceans. — Trilohites, the highest species of the Cambrian seas yet 

 discovered, were of many species and very diverse forms. Figs. 535, 536 rep- 

 resent some of the species of the genus Olenellus ; Fig. 535, 0. Vermontanus 



535. 



533-539. 

 534. 



539. 



536. 



Teilobites. — Fig. 533, Agnostus nobilis, two middle segments absent (1) ; 534, Microdiscus speciosus (2) ; 

 535, Olenellus (Mesonacis) Vermontanus (1) ; 536, Olenellua Thompson! (1, i max. size) ; 537, Bathy- 

 notus holopyga, distorted (1) ; 538, Olenoldes Fordi, head-shield without the cheek (2) ; 538 a, separated 

 cheelj; 538 b, same, pygidium (caudal extremity); 539, Ptychoparia Adamsi. Figs, from Walcott; 

 533, after Ford. 



Walcott ; Fig. 536, 0. Thompsoni HalL These species from Georgia, Vt., are 

 over six inches long ; the latter occurs also in western Newfoundland. The 

 Olenellus Gilberti Meek (Fig. 540) is a fine species from Nevada and Utah. 

 Another large species, 0. asaphoides of Emmons, is from near Bald Mountain 

 and Troy, Washington County, N.Y. Emmons cited it as characteristic of 

 the "Upper Taconic." The Batliynotus (Fig. 537), remarkable for the long 

 spines of its head-shield, is another Trilobite of large size, from Georgia, Vt. 

 The genera Agnostus and Microdiscus include small species, differing in the 

 former having two segments between the head and caudal shield, and the 

 latter three. 



