Dr. F. R. Gowper Reed — The genus Homalonotus. 275 



but this reference seems unwarranted, the head-shield so far as we 

 know it not possessing any of the typical characters. The definition 

 of Koenigia given by Salter' was as follows : " Convex ; head wide, 

 transverse, with concave and tricuspidate front, glabella subquadrate, 

 well-defined; eyes rather approximate, on gibbous cheeks; tail 

 pointed, many ribbed." Salter^ described the species H. Knighti 

 at some length, but he did not give a clear description or figure 

 of the peculiarly characteristic structure of the anterior part of 

 the head-shield, which is well seen in some British specimens. 

 Moberg & GronwalP published some better illustrations of this 

 trilobite, and showed distinctly the peculiarities of the anterior 

 margin and the course of the facial sutures. It is seen that the 

 remarkable tricuspid front is due to the median projection of the 

 anterior end of the epistome (= rostral shield) which is bounded on 

 each side on the inferior surface by the epistomal sutures. The 

 triangular lateral projections are formed by the anterior ends of the 

 free-cheeks being angulated forwards, and also bent up and down in 

 a zigzag manner. The marginal doublure thus has an unusual 

 angulated appearance in a frontal as well as in a superior view. The 

 facial sutures unite by a transverse commissure before a very narrow 

 pi'e-glabellar area, and this transverse suture (which must be regarded 

 as the direct continuation of the true facial sutures bent rather 

 suddenly inwards) consists of two gently sigmoidal halves meeting in 

 tlie middle at an angle so as to form a small median point. The 

 sudden change in the direction of the facial sutures maybe due to the 

 more rapid forward growth of the lateral portions of the head-shield 

 as com^pared with the median portion, and may be directly connected 

 with the anterior projection of the front ends of the free cheeks on 

 the margin. 



A similar tricuspid front and projecting epistome is found to exist 

 in the species H. Joharmis, Salter,* as an examination of the types 

 and other specimens from the original locality in the Jermyn Street 

 Museum proves ; Salter did not show this tricuspidation in his figures, 

 the anterior end of the epistome of his specimens being imperfect, 

 and the lateral projections of the anterior margin of the head-shield 

 being blunter and less prominent than in S. Knighti. But he 

 figured the inferior doublure and epistomal sutures clearly in his 

 figures 2 and 7. 



A character of some importance which is present in S. Knighti 

 and less distinctly in H. Johannis, is the more or less circumscribed 

 subquadrate or rounded area on each side of the base of the glabella. 

 These areas are differently ornamented to the rest of the head-shield, 

 and resemble in position and shape the '"alar" areas of Ilarpes. 

 But to avoid prejudging their homology they are here termed the 

 paraglalellar areas. We shall have occasion to remark on their 

 presence in other subgenera. 



1 Salter, Men. Brit. Trilob., p. 106. 

 " Ibid., p. 119, pi. xii, figs. 2-10, pi. xiii, fig. 8. 



^ Moberg & Grdnwall, Om Fyled. Gotl., Lunds Univ. Arssk., N.F., Af. ii, 

 Bd. v, No. 1, pp. 72-7, pi. v, figs. 1-4, 1909. 

 * Salter, op. cit., p. 117, pi. xiii, figs. 1-7. 



