752 THE PALEONTOLOGY OF MINNESOTA. 



(.Observations on Lichas. 



like Phacops, Trinucleus, etc., or a slightly oscillating group like Proetus, but the 

 plastic Lichas, presenting the widest range of variation, affords an excellent 

 opportunity for empiric skill at classification. 



The typical species of the genus Lichas is the L. laciniatus (Wahlenberg)* 

 Dalman, founded upon a pygidium, an outline copy of the original figure being 



Fig. 74. Outline of pygidium of Lichas laciniatus Wahlenberg (after Dalman). 



introduced in this place. The remaining structure of the species is not known; but 

 the pygidium bears two broadly falciform extensions on each side, and terminates 

 in a single acute undivided median lobe. It is quite similar to the pygidium referred 

 to Platynotus trentonensis Conrad, given by Halljf and if the imperfect cephala from 

 the Trenton limestone of New York given by this author represent the same species 

 as the entire individual quoted and figured in the work cited as from the blue lime- 

 stone of Ohio, the cephalic structure of Lichas in its typical or restricted meaning is 

 very simple, the lateral furrows debouching at right angles in the occipital furrow, 

 there being no middle grooves and no third lobes.J This is the structure of the New 

 York specimens of L. trentonensis, of which the pygidium is not definitely known, 

 that referred by Hall (loc. cit., fig. Ib) to this species, being probably a part of our 

 Conolichas cornutus. This structure, however, is the same as that predicated of 

 Platymeiopus Angelin (as interpreted by Schmidt). We have therefore to face a 

 dilemma in the application of these terms. The precise value of the restricted term 

 Lichas is not yet demonstrated, but knowing the meaning of Platymetopus we may 

 provisionally employ the term while awaiting fuller evidence of its relation to the 



Uebcr die Palaoaden, pp. 53, 71, 72, pi. vi, fig. 1, 1828. 

 + Palaeontology of New York, vol. 1, pi. cxiv, fig. le. 



tTo Illustrate the normal lobatlon of the cephalon In the highest development of the llchad type of structure a figure 

 is here reproduced of the L. palmata Beyrlch. (Barrande, Syst. 811 , vol, I. pi. xxvm. fig. 45,) 



Fig. 75. Glabclla of Lichas palmata Beyrlch. (After Barrande.) 

 d. dorsal furrows. 

 a. median or frontal lobe. 



1', 2', 3'. anterior median and posterior lateral lobes. 

 J, 9, ). apterior median and posterior lateral furrows. 



