BELTELLA VERISIMILIS. 107 



I have not found any really good specimens of this species in the Belt 

 Collection at the British Museum. I. 7592 bore the specific name, but it is clear 

 that the label had at some time been misplaced, for this specimen (see Plate VI, 

 fig. 6) corresponds with Belt's description of " Conocoryphe ? longispina." More- 

 over, it shows the tail, while Belt states that the tail of his " Conocoryphe ? 

 bucephala " is unknown. 



Mr. G. J. Williams has, however, obtained a number of fragmentary speci- 

 mens which agree with Belt's description of the species and come from the same 

 horizon ; and there can be very little doubt that they belong to B. bucephala. 



But the best specimen that I have seen is that figured in Plate XII, fig. 11, 

 which Salter in 1373 called Conocoryphe williamsoni, n. sp. It is somewhat 

 remarkable that he should have used the same name that Belt had previously 

 given to an entirely distinct species; but possibly he had come to the conclusion 

 that Belt's Gonororyphe ? williamsoni was not a Gonocoryjihe. In any case, Salter's 

 Conocoryphe williamsoni differs from Belt's species of the same name, but, on the 

 other hand, agrees with Belt's Conocoryphe ? bucephala. 



Belt describes the glabella as subcorneal, truncated, very prominent; but in 

 his figures it is rounded in front rather than truncate. According to him, it is 

 " without furrows when perfect ; but when crushed, or divested of outer crust, 

 showing two pairs of internal ones." Some of the specimens that I have seen 

 support this view, but they are hardly conclusive. In his description Belt gives 

 the number of thoracic segments doubtfully as fourteen, but his figure shows 

 only twelve. 



In its general form and proportions B. bucephala is very like B. depressa, and 

 in distorted specimens it is not always easy to distinguish between the two. In 

 B. bucephala, however, the glabella is conical and rounded in front, while in 

 B. depressa it is more quadrate and truncate in front. In the former, moreover, 

 the eye is a little farther forwards than in the latter. These appear to be the only 

 differences that survive compression and distortion. 



In B. verisimilis both the head and thorax are longer in proportion to their 

 width. The glabella also is more elongated and the eye is set considerably farther 

 forwards and closer to the glabella. 



Horizons and Localities. — Upper part of the Middle Lingula Flags: Nant 

 Cistfaen, Arenig. Upper Lingula Flags : Rhiwfelyn, Mawddach. 



3. Beltella verisimilis (Salter). Plate XIII, figs. 1—5. 



1866. Conocoryjme ! verisimilis, Salter, Mem. Geol. Surv., vol. iii, p. 308, pi. vi, fig. 13. 



Head approximating to a semicircle, but somewhat elongated, with the length 

 more than half the width. Glabella long, tapering slightly forwards, rounded in 

 front, separated from the anterior margin by a frontal limb of considerable width ; 



