76 PALAEONTOLOGY OF NEW YORK. 



is shown by the size of some of the fragments of the head, for in the genus 

 Lichas the cephalon is usually very short in comparison with the length of 

 the thorax and pygidium. An appearance of considerable length in this 

 part is sometimes produced by a very protuberant and elevated glabella as 

 in Lichas celorhin and others; but it is found on a careful comparison of the 

 dimensions of the head, thorax and pygidium, in the rare instances of species 

 in which the parts have been preserved in juxtaposition (Lichas Boltoni, L. 

 palmata, L. scabra, L. gibbus), that their proportional length is as 1 to 1.6 to 1 

 (not inclusive of spines); and upon this basis a restoration of Lichas grandis 

 from the very large fragment of a cephalon figured on plate xviii, indicates 

 thai the entire length of the animal to the extremity of the tail-spines would 

 have been about 480 mm., or upwards of 19 inches. This estimate is in 

 harmony with the relative proportions of the cephalon and pygidium fur- 

 nished by the type specimen of Lichas superbus, Billings. In the descrip- 

 tion of L. superbus (Billings, Inc. tit.), mention is made of a fragment of the 

 cephalon in which the frontal lobe has a length of three inches. This 

 would be one-third larger than the frontal lobe in the individual here 

 restored, and if the increase in the size of this part was accompanied by the 

 same relative increase in the length of the animal, this fragment belonged 

 to an individual probably not less than two feet in length, a size unequaled 

 by that of any other known trilobite. 



Observations. The marked prominence of the anterior lobe and the some- 

 what suppressed lateral lobes of this species suggest a similarity to forms 

 of the genus Acidaspis, and this feature, together with the striking spinose 

 character of the pygidium, led to the temporary reference of the species to 

 that genus in the Illustrations of Devonian Fossils (ioc. cit.). The character 

 of the subdivisions of the glabella appears, however, to be more in harmony 

 with those of Lichas, and similar in general features to those of L. Eriopis, 

 /,. hylaus, L. gryps and L. dracon. The pygidium of Lichas, though usually 

 with hut three pairs of spines, occasionally has four (L. Eriopis, L. ptyonurus), 

 while in Acidaspis the pygidium is very short, with two long postero-lateral 

 spines and a fringe of shorter spines, and is not subject to much variation. 



