PLATE XXX— Coutinued. 



Fig 18 A larger example, retaining the "manubrium." 



Hamilton group. Pratt's Falls, Onondaga county. 

 Fi* 19 A specimen in the shale, from which the crust has been removed, showing the thickness of this 

 c ,.„st over the crown and its comparative tenuity on the basal portion of the mandible. 



Hamilton group. Pratt's Falls, Onondaga county. 



Pal^opal.kmun Xewberryi. 



1'age 203. 

 Fiir 20. Lateral view of the type specimen, natural size. 



ml 21 The same view, enlarged to two diameters, showing the somewhat crushed and broken carapace, 

 the bases of the strong antennas, the basal portion of an ocular peduncle, a joint of a maxillary 

 n a lv,us(1) and fragments of five pairs of ambulatory appendages. The abdomen is incurved, 

 and is composed of five somites, the first two of which bear the bases of natatory appendage,. 

 The tail is expanded, and the posterior portion of it has been abraded. 

 Fig. 22. Dorsal view of the same specimen, natural size, showing the prominence of the antenna-, the 



carina on the carapace, and the incurvature of the abdomen. 

 Fig 23 The tail, enlarged to two diameters, showing the broad, stout telson, the lateral spmes with then- 

 short basal joints, and the flat, tenuous lamellar spines lying in the membranous expansion. 

 Erie shales. (Portage group.) LeRoy, Lake county, Ohio. 



Tkopidocakis IIamiltoni.k, ii. sp. 



Fig. 24. The type specimen, natural size. , 



Fig 25 The same, enlarged to two diameters. The specimen is folded along the hmge-lme, the edge of 

 the right valve being seen within the ventral margin of the left. The outline of the carapace 

 is closely similar to that of T. bivaHnata of the Chemung group, being narrow near the ante- 

 rior extremity, rapidly widening posteriorly. Both dorsal ami ventral margins are elevated 

 and ornamented by transverse striatums. A single nearly straight carina lies on the middle of 

 each valve, and this is also striated along its summit. An eye-node is visible near the anterior 

 extremity of this carina. . 



This specimen was obtained too late to permit a notice of the species in its proper place m the text. 

 Hamilton group. In the uppermost beds of the shales. Foster's, Canandaigua Lake. 



