PLATE X 

 TRINUCLEUS CONCENTRICUS Eaton (Pages 222-225) 



Figure 1. — Cephalon of young individual, without genal spines ; 

 showing ocular ridges and two rows of perforations around anterior and 

 lateral borders. X 40. 



Figure 2. — Cephalon of younger individual before the growth of the 

 perforate border ; showing distinctly the clavate ocular ridges, a, a. X 40. 



Figure 3. — Pygidium of young individual; showing the indistinct 

 limitation of axis and the elevated transverse ridges of the pleura and 

 axis. X 40. 



Figure 4. — Thorax and pygidium of an entire specimen from which 

 the dorsal test has been removed by weathering, exposing below the 

 fringes of the exopodites, which entirely cover the pleural portions. The 

 stronger lines ascending from the axis are the main stems of the exopo- 

 dites. The black dots along the axis are the fulcra for the attachment 

 of the limbs. X 4. 



Figure 5. — One-half the pygidium with three attached thoracic seg- 

 ments, from an entire specimen, with a portion of the test removed ; 

 showing the highly developed, lamellose fringes of the exopodites. X H- 



Figure 6. — -The same; lower side ; showing the short, stout, phyl- 

 lopodiform endopodites, a, and the long, slender exopodites, b, bearing 

 the lamellose branchial fringes. In the lower third of the figure the ends 

 of the joints of the separate endopodites are shown by the oblique ascend- 

 ing rows of setiferous nodes. The small ovate organs, c-, along the side 

 are provisionally correlated with the exopodites. A narrow striated 

 doublure margins the pygidium and the ends of the thoracic 

 pleura. X 11. 



Utica Slate, Ordovician, near Rome, New York. 



