108 BRITISH CAMBRIAN TRILOBITES. 



with two pairs of oblique glabellar furrows, often indistinct ; neck-furrow almost 

 obsolete and neck-segment consequently ill-defined. Eyes small, set very near to 

 the glabella, much nearer to the anterior than to the posterior margin, but never- 

 theless some distance behind the anterior end of the glabella. Facial suture 

 curving inwards and backwards from the anterior margin to the eye, and thence 

 running outwards and backwards, nearly in a straight line, to the posterior 

 margin, which it cuts at a distance from the glabella about equal to half the width 

 of the latter. Fixed cheeks narrow, even at their base. Free cheeks somewhat 

 crescentic, with a broad, down-turned margin, which is produced posteriorly into 

 a genal spine running directly backwards. 



Thorax consisting of twelve segments. Axis in the earlier segments wider 

 than the pleurae, in the later segments not quite so wide. The pleurae of the first 

 segment extremely short, only about half the width of the axis ; in the later 

 segments longer, bent downwards and backwards about half-way out from tlie 

 axis, apparently with falcate terminations ; pleural grooves rather sharp. 



Tail small, semicircular, slightly emarginate behind. Axis forming about a 

 third of the total width, with one ring clearly defined and a second indistinctly 

 indicated. Lateral lobes flat, with two oblique furrows on each side. 



Dimensions. — The type-specimen, when complete, must have been about 

 38 mm. in length. 



According to Salter the glabella is entirely destitute of lobes. But his descrip- 

 tion seems to be based on the specimen shown in Plate XIII, fig. 1, and its condition 

 is too imperfect to allow of any safe conclusion on this point. The specimen 

 represented in Plate XIII, fig. 3, is amongst those referred by Salter to B. drpressa ; 

 but the glabella is too elongated and too much rounded in front, the eyes are too 

 far forwards, and the pleurae of the first thoracic segment are too short for that 

 species. 



B. verisimilis is in general easily distinguished from B. depressa and B. buce- 

 phaln by its elongated glabella and the more forward and approximate position of 

 the eyes. The vagueness of the neck -furrow also seems to be a feature of some 

 value, but in crushed and distorted specimens the apparent presence or absence of 

 furrows of any kind is not a reliable character. In the thorax the greater length, 

 in proportion to the width, and the extreme shortness of the first thoracic pleura?, 

 are the most important distinguishing features. 



It is no doubt probable that the specimens from the Middle Lingula Flags are 

 not specifically identical with the Tremadoc form, though they are hardly perfect 

 enough to admit of definite separation at present. Moreover, the fact that a 

 narrow form of Beltella with long glabella, forwardly-placed eye, obscure neck- 

 furrow, and very short first thoracic segment occurs both in the Middle Lingula 

 Flags along with B. bucephala and in the Tremadoc along with B. depressa, 



