752 THE PALEONTOLOGY OF MINNESOTA. 
LObservations 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 Hall;+ 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.{ 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. 1b) to this species, being probably a part of our 
Conolichas cornutus. This structure, however, is the same as that predicated of 
Platymetopus 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 
* Ueber die Palewaden, pp. 53, 71, 72, pl. vi, fig. 1, 1828. 
+ Palzwontology of New York, vol. i, pl. Cxrv, fig. le. 
% To illustrate the normal lobation of the cephalon in the highest development of the lichad type of structure a figure 
is here reproduced of the L. palmata Beyrich. (Barrande, Syst. Sil, vol, i, pl. xxv, fig. 45,) 
Se. 
<< 
a 
\ 
\ 
Fig. 75.—Glabella of Lichas palmata Beyrich.™ (After Barrande.) 
d. dorsal furrows. 
a. median or frontal lobe. 
1', 2!, 3!, anterior median and posterior lateral lobes. 
1, 2,3. anterior median and posterior lateral furrows. 
