BRITISH FOSSILS. 



Decade XI. Plate II. 



STYGINA LATIFRONS. 



[Genus STYGINA, Salter, 1852. (Sub-kingdom Articulata. Class Crustacea- 

 Order Trilobita. Family Asaphidae.) Body ovate, flattened ; head and caudal shield 

 nearly equal ; body of nine rings ; eyes small, placed far backward and inward, near the 

 base of the glabella, which is quite distinct above, and much contracted below. Facial 

 suture marginal along a wide space in front, and below the eyes curved outward and 

 ending on the posterior margin. No rostral shield. Labrum convex, entire. Axis of 

 body narrow. Pleurae without furrows. Caudal shield with a long axis.] 



Diagnosis. *S'. sesquiuncialisy ovalis, axi migusto ; spinis capitis 

 hrevissimis. Caput semiovale, obtusum, glabella ad basin angustissima, 

 oculis retror sis, fere ad basin capitis retractis, Cauda semiovalis, obtusa, 

 axi subannulato. 



Synonyms. Asaphus latifrons, Portlock, Geol. Rept. Londonderry 

 and Tyrone, pi. 7, figs. 5, 6. A. marginatus, ib., fig. 7. Stygina latifrons, 

 Salter (1852) in Rep. Brit. Assoc. Trans. Sect. p. 59. Id. Siluria," 1st 

 ed. 18, and 2nd ed. 1859, p. 184, Foss. 26, fig. 2. 



Among the many new and interesting forms of Trilobites de- 

 scribed by Colonel Portlock in his work on Londonderry and 

 Tyrone, a small species of A saphus is recorded from the Lower 

 Silurian of Tjnrone, which he named A. latifrons, distinguishing it 

 from some other species by the breadth of front included within the 

 curve of the facial suture. The species is remarkable for the position 

 of the eyes, which are placed far backward and inward, so as to be 

 close to the base of the small and narrow glabella. This pecuharity 

 of habit is associated with some other characters which will remove 

 the species from Asaphus. The flattened oval form, long axis to the 

 tail, and the head spines, much resemble those of Asaphus, from 

 which the nine ungrooved pleurae effectually distinguish it. In the 

 partial obliteration of the glabella, number of body rings, and course 

 of the facial suture, it is closely allied to Jllcenus, from which its habit 

 diflfers so much ; and there is enough of the under side preserved 

 to show there was no rostral shield, which last is an essential 

 character of Illmnus. 



[xi. ii.] 11 B 



