BELTELLA DEPRESSA. 105 



downwards and backwards; pleural grooves broad and deep; the anterior pleurae 

 ending- in short points, the later pleurae produced into backwardly directed spines. 



Tail small, semicircular. Axis forming about a third of the total width, almost 

 reaching the posterior border, and ending bluntly ; with one ring clearly marked 

 off and two others indistinctly indicated. Lateral lobes with two furrows on each 

 side. No defined margin. 



Dimensions. — Specimens of ordinary size are about 35 mm. long ; but the 

 thorax and tail figured in Plate XII, fig. 6, belong to an individual which must 

 have been about 70 mm. in length. 



In Salter's original specimens the earlier thoracic pleurae seem to have rounded 

 terminations, and the later pleurae to be truncate ; but the appearance is fallacious 

 and is due to the fact that the actual ends of the pleurae are buried in the matrix. 

 That this is the correct interpretation is, I think, clearly shown by the specimen 

 figured in Plate XII, fig. 9. On the right-hand side of this specimen the apparent 

 terminations of the pleurae are similar to the apparent terminations in the type- 

 specimen, and seem to be rounded or truncate. But the left-hand side shows that 

 the anterior pleurae end in short points, and the later pleurae are produced into spines. 



B. depressa is distinguished from B. verisimilis and B. bucephala by its square 

 and somewhat truncate glabella. From B. verisimilis it is further separated by 

 the more backward and rather more distant position of the eyes, and by the greater 

 width of the head and thorax in proportion to their length. B. bucephala 

 approaches it more closely in its proportions ; but in that species the glabella is 

 narrower, more conical, and well rounded in front, and the eyes are set a little 

 more forwards. 



Salter's Goliocorijphe vexata is probably an imperfectly preserved Beltella 

 depressa. In their general form and proportions the head and glabella show no 

 recognisable differences, and the characters on which Salter relies to distinguish 

 the species are the absence of glabellar furrows and the nearness of the eyes to the 

 glabella. But the state of preservation is such that the glabellar furrows may well 

 have been lost, 1 and with regard to the eyes I do not find any decided difference. 

 The specimen is slightly distorted, and on the right-hand side the eye is nearer to 

 the axial furrow than in B. depressa, but on the left-hand side it is at about the 

 same distance. 



Brogger 2 has suggested that this species may belong to Oyclognathus, but he 



1 It is worthy of note that Belt (G-eol. Mag., vol. v, 1868, p. 10) says that in his Conocoryphe 

 bucephala and Salter's C. depressa the glabellar furrows are only seen in specimens which have been 

 compressed or have been deprived of their test. 



2 Die Silur. Etagen, 2 u. 3, p. Ill ; see also Verb. d. Eidoma-Niobe-F&una,, Nyt Mag. f. Naturvid., 

 vol. xxxvi (1897), p. 198 — separate copies (1896), p. 35. It would appear from his remarks in the 

 latter paper that the author had seen the specimens in the Jerniyn Street Museum, but he does not 

 profess to have examined them closely. 



15 



