CONTRIBUTIONS TO PALiEONTOLOGY. 225 



The cheeks and thoracic articulations are unknown. 



One imperfect head measures nearly five inches across the base, 

 with a length of three and a half inches, being incomplete in 

 both directions. A portion of another head is quite as large in 

 the parts preserved. Another smaller and imperfect specimen 

 has a width at base of nearly three inches, with a length of 

 more than two and a half inches to the occipital furrow. The 

 anterior lobe of the glabella in this one is an inch and three- 

 eighths in its longitudinal and transverse diameters, and its 

 elevation above the frontal limb ( which is broken awa}^) has 

 probably been greater than the diameter. The upper side of this 

 lobe is worn off, but it still has a height above the surrounding 

 groove of three-fourths of an inch. 



The length of the body of one of the pygidia, to the division 

 of the two posterior spines, is two and a half inches, and the 

 width on the anterior margin is three inches. 



This ex.travagant trilobite presents, to some extent, the cha- 

 racters of LicHAS ; but in the pygidia with four lobes, and four 

 spines on each side, there is a departure from the typical forms 

 of the genus. The distinctly rounded and widely separated an- 

 terior lobe of the glabella, without adjacent lateral lobes, offers 

 also some points of distinction from Lichas. 



These characters, however, are in some degree approached by 

 Lichas pustulosus of the Lower Helderberg group ( Pal. N.York, 

 Vol. iii, pa. 368, pi. 78 ), the pygidium of which presents four 

 divisions upon the margin. 



In the elongate primary and secondary tail -spines, the Scho- 

 harie grit species resembles some forms of Acidaspis ; as well also 

 in the extreme ornamentation of the head, though not in the 

 disposition of its parts. 



The most extravagant European form of the genus, the Lichas 

 (Arges) armata of Goldfuss, still preserves the distinctive generic 

 features of the head, though the characters of the pygidium are 

 less distinctive. 



In the examples under co^^k|||tion, there are so many peculiarities, 

 that it may be found necess^^Sft^pia distinct generic name; in which 

 case, I would propose Tera'^ '^''Uidigium ; and aomg, scutum. 



[Senate, No. 115.] 



>ose Tera'" '^''^digiu 



