200 Dr. Ivor Thomas — Trilohite Fauna of Devon and CormcaU. 



Peoetus, sp. c. PI. VII, Fig. 9. 



Bescription. — The general outline of the pygidium is semicircular, 

 and has a length of about 5 mm. and greatest breadth of about 10 mm. 

 The broadly convex axis has ten rings, and tapers very quickly from 

 the anterior portion, where the width is nearly as great as the whole 

 length of the axis. The flattened pleura curve slightly backwards 

 and number at least ten. Some of the better preserved parts show 

 indications of a subdivision of each pleuron into two portions by 

 a narrow furrow. The marginal border is very narrow, but well 

 defined. 



Locality and Horizon. — As the preceding form. 



Remarks. — Compared with Proetus, sp. h, the axis of the latter is 

 less tapering, the segments both in the axis and pleural region are 

 fewer, and the marginal border is much broader. 



Dechenella. tjssheei, sp. nov, PI. YII, Fig. 10. 



Description. — The cephalon is almost semicircular, and possesses 

 a narrow, flattened marginal border. The straight posterior margin 

 forms the greatest breadth, and measures approximately 6'5 mm., 

 while the greatest length of the head-shield is about 4 mm. An angle 

 of nearly 70° is enclosed bj' the genal extremity, which is not produced 

 into a spine. 



The prominent, roughly triangular, and fairly tumid glahdla is 

 well demarcated, and tapers considerably towards the rounded frontal 

 margin. The angle formed by the bounding dorsal grooves anteriorly 

 = 41° approx. Three well-marked pairs of lateral f urroAvs are present, 

 the anterior pair being the shortest and of least depth, while the 

 posterior furrows are very deep and run in a low curve to the occipital 

 groove. In this manner two tumid, triangularly shaped lobes are 

 separated off at the posterior portion. The occipital ring is only 

 partly preserved, but appears to have been fairly prominent and 

 narrow. 



The facial sutures cut the anterior border at a distance of nearly 

 3 mm. apart. They run gradually outwards from this point of inter- 

 section, then curve inwards posteriorly to within a short distance of 

 the glabella, and after a slightly curved course turn outwards rather 

 sharply, reaching the posterior margin at a low angle about two- 

 thirds of the distance between the base of the glabella and the genal 

 angle. The eyes are not preserved. 



The cheeJc-areas are elevated to almost the height of the glabella, 

 and gradually slope outwards to a flattened region adjacent to the 

 marginal border. 



Locality and Horizon. — The same as Phacops (Trim.) tripartitus, 

 sp. nov., etc. 



Remarhs. — The name Lechcnella was first employed by Professor 

 Kayser (11, p. 703) for those members of the Proetidre with very 

 tapering and strongly lobed glabella. 



The glabella of our form shows a certain resemblance to that of 

 Dechenella verneuili (Barr.), as interpreted by Professor Kayser (11, 

 p. 705, pi. xxvii, figs. 1-5). In most other respects the two forms 

 differ considerably. Thus the British specimen has no genal spine, 



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