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.) 
Ampyzx 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 ; g/abella 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, pleurze 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 33 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 aad 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 Here 
glabella in front, towards the lateral angles Cephalicahi qa 
cutting the posterior margin a little within ing the eyes and 
the angles, and usually exhibiting a small diagonal facial su- 
ocular (?) tubercle in the middle. Types ‘es- 
of the genus Trinucleus seticornis (His.) sp., T. Bucklandi 
(Bar.), &e. 
In my ‘ Synopsis of the Silurian Fossils of Ireland’ I pointed 
