410 Prof. F. M'Coy on the Classification of 



head, thorax and pygidium almost equal ; cephalic shield 

 slightly more than twice as wide as long, lateral angles very 

 short ; eyes half their length from the axal furrow ; pygidium 

 depressed, length rather more than half the width, axis two- 

 thirds the length, conical, segmental furrows one on each side, 

 obtuse. Length 11 lines. 

 Black Wenlock shale of Builth. 

 {Col. University of Cambridge.) 



Ampyx latus (M'Coy). 



Sp. Char. Entire animal transversely ovate, length one-fifth less 

 . than the width ; cephalic shield smooth, front margin regularly 

 curved, width three-fifths the length ; glabella moderately tu- 

 mid, pyriform, having a narrow vertically elongate (? ocular) 

 swelling close to the middle third of each side, and two short, 

 minute segmental furrows at each side of the narrow base ; 

 thoracic segments five, pleurae of each side twice the width of 

 the axal lobe ; pygidium very obtusely and regularly rounded, 

 four times wider than long, axis with about seventeen minute 

 segmental furrows, sides with about eight. Length of entire 

 animal 3| lines. 



This rare species is most allied to the A. parvulus (Forb.) and 

 the A. nasutus (Dal.), from both which the perfect animal is 

 easily known by its transversely oval form ; the regular curvature 

 and great width of the cephalic and pygidial shields easily distin- 

 guish those parts when found separate ; the latter agrees nearly 

 in form with that of the A. parvulus, from which it differs equally 

 with the former in all the other characters of cephalic shield, &c. 



Rare in the black Wenlock shale three miles north of Builth. 



(Col. University of Cambridge.) 



Tretaspis (M'Coy), n. g. 



Gen. Char. General characters of Trinucleus, but having only five 

 body-rings, the base of the glabella having 

 two short segmental furrows at each side, 

 and the cheeks being traversed diagonally by 

 a nearly straight eye-line, extending on each 

 side from the junction of the cheeks and 

 glabella in front, towards the lateral angles cephali/aSSd show- 

 cutting the posterior margin a little within i n g the eyes and 

 the angles, and usually exhibiting a small diagonal facial su- 

 ocular (?) tubercle in the middle. Types tures. 

 of the genus Trinucleus seticornis (His.) sp., T. Bucklandi 

 (Bar.), &c. 

 In my ' Synopsis of the Silurian Fossils of Ireland ' I pointed 



