CTENOPYGE EXPANSA. 87 



recognised species of the genus. No other tail of the same type is known, while 

 in the thorax the very narrow axis and wide pleural lobes tire alone sufficient to 

 distinguish it from the majority of the other forms. Only Gt. expansa approaches it 

 in these respects. In that species the axis is even narrower in proportion to the 

 pleurae, and the pleura? are specially characterised by thread-like ridges along the 

 anterior and posterior borders, and by the position of the pleural groove. 



The free cheek also is quite unmistakable. In Spliserophthatiuus and Gtenopyge 

 generally the cheek-spine springs from the middle of the external margin ; but in 

 the other species the spine at its origin is nearly at right angles to the margin, 

 while in Gt. peclen it makes so small an angle that the outer edge of the spine is 

 almost the direct continuation of the outer edge of the cheek. 



But the cranidium by itself is not very easy to recognise. It is usually more 

 strongly emarginate than in Ct. bisulcata, Gt. fulcifera and Gt. directa; but as 

 shown in Plate IX, fig. 7, this character is not always very clearly seen. The fixed 

 cheek at the eye is about equal in width to the glabella, as in Gt. fa 1c if era, while in 

 Gt. directa and Gt. teretifrons it is wider and in Ct. bisulcata it is narrower. The 

 ocular ridge makes about the same angle with the axis as in Gt. file if era, in Gt. 

 bisulcata the angle is smaller, and in Gt. directa and Gt. teretifrons it is larger. The 

 eye appears to be longer than in other species, so that although the front is well 

 forwards the back is as near to the posterior margin as in Gt. bisulcata. The 

 facial suture cuts the anterior margin nearer to the glabella than in Ct. bisulcata ; 

 behind the eye it turns almost parallel to the posterior margin, meeting the latter 

 at a very acute angle; in Ct. bisulcata and Gt. falcifera it bends back near its 

 extremity so as to make a considerable angle with the margin, while both in Gt. 

 directa and Gt. teretifrons its course behind the eye is much more oblique, more 

 backwards and less outwards. 



Horizon and Localities. — Upper Lingula Flags : Malvern. 



5. Ctenopyge expansa (Salter). Plate X, fig. 8. 



1873. Olemts expansus, Salter, Cat. Canib. Sil. Fuss. Mus. Cambridge, p. 12. 



1900. Olenus (Ctenopyge?) expansus, F. E. C. Eeed, Geol. May. [4], vol. vii, p. 306, pi. xii, tigs. 2, 3. 



Of this species only the thorax is known with certainty, but the specimens may 

 possibly include a part of the tail. Salter's types have been described and figured 

 by Mr. Reed. 



In the best specimen portions of ten segments are visible, but it is not clear how 

 much belongs to the thorax and how much to the tail. The axis is narrow, less 

 than one-third the width of the pleura), almost parallel-sided, with very faint indi- 

 cations of median tubercles. The pleurae are flat, with a thread-like ridge near the 

 anterior border and another very close to the posterior border; the pleural groove 



