BELTELLA VERISIMILIS. 109 



strongly suggests that these characters are not specific but sexual. It seems 

 probable, accordingly, that B. verisimilis is not a distinct species but is the other 

 sex of B. bacephala and II. depressa, or, to be more precise, B. verisimilis (Salter) 

 is the other sex of B. depressa, and the Middle Lingula forms that I have pro- 

 visionally included in B. verisimilis belong to the other sex of B. bucephala. 



Imperfect specimens sometimes bear a striking general resemblance to speci- 

 mens of Angelina sedgwiclci, or even of Olewis cataractes, which have been strongly 

 compressed from side to side. It is difficult in such cases to judge the true 

 relative widths of the axis and the side-lobes, and glabellar furrows may easily be 

 obliterated. Perhaps the most reliable characters to depend upon are the number 

 of thoracic segments and the position of the eyes, which is more forward in B. 

 verisimilis than in either of the other species. 



B nigger 1 has suggested that this species, as well as B. depressa, may belong to 

 Cyclognathus. But although the type specimen is decidedly obscure in many 

 respects, the presence of genal spines, the comparative narrowness of the glabella 

 and thoracic axis, the position of the eyes distinctly behind the anterior end of the 

 glabella, and the course of the facial suture, are sufficient to distinguish it from that 

 genus. 



Reed 2 refers it to Angelina, and to that genus it offers several points of resem- 

 blance. The width of the frontal limb, the vagueness of the neck-furrow, and the 

 apparent absence, in the type specimen, of glabellar furrows, are features which it has 

 in common with Angelina. But, as Reed remarks, the number of thoracic segments 

 is twelve instead of fifteen, and the eyes are too far forwards. Reed thinks that 

 these characters may be due to immaturity, but they are not present in undoubted 

 specimens of Angelina of considerably smaller size. If I am right in referring the 

 specimen figured in Plate XT1I, fig. 3, to the same species, the presence of 

 glabellar furrows at once removes it from Angelina. In any case, even in the 

 type specimen, the side-lobes are much narrower, as compared with the axis, 

 than in Angelina, and the very short pleurae of the first thoracic segment are also 

 a distinguishing feature. 



Belt 3 considers B. depressa and B. verisimilis to be the same species in different 

 states of preservation. He thinks that the outer surface of the test was smooth, 

 and that glabellar furrows are shown only on the internal cast or when the 

 specimen has been crushed. 



Horizons and. Localities. — Middle Lingula Flags : Trinant and Nant Cistfaen, 

 Arenig (these are the specimens figured in Plate XIII, figs. 4 and 5, which may 

 be distinct from the Tremadoc form). Lower Tremadoc : Penmorfa. 



1 Die Silur. Etagen 2 u. 3, p. Ill ; Verb d. Euloma-Niobe-Fnunii, Nyt Mag. f. Naturvid., vol. 

 xxxvi (1897), p. 199— separate copies (1896), p. 36. 



2 Geol. Mag. [4], vol. vii (1900), p. 256. 



3 Loc. cit., vol. v (1868), p. 10. 



