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



Cer auras Williamsii (M^Coy). 



/Sp. Char. Cephalothorax semielliptical, length rather more than 

 half the width ; glabella semicylindrical, gibbous, rounded in 

 front, with nearly parallel sides, three nearly equidistant, 

 curved, segmental furrows on each side, the basal pair nearly 

 confluent at their ends with the neck-furrow, inclosing a 

 tumid ovate space on each side, separated by an undivided 

 space about one-fourth of the width of the glabella ; thorax 

 twice the length of the glabella, axal segments large, two- 

 thirds the width of the pleurse, each of which has a very large, 

 diagonally cleft, oblong tubercle at its origin, beyond which 

 there is a neck-like contraction of the margin, followed at one- 

 third from the axis by a hemispherical tubercle about half its 

 diameter distant from the first, beyond which the distal two- 

 thirds of each pleura is falciformly dilated into a thin, flat, 

 fin-like appendage, the anterior margin of which is very con- 

 vex, posterior margin slightly concave, extremity pointed ; py- 



- gidium small, the six marginal spines small, all extending to 

 about the same distance backwards, the anterior pairs there- 

 fore longest ; they are thick, triangular, and three or four times 

 wider than the others. Length of entire animal 1 inch 4 lines, 

 of glabella 5 lines, width about 9 lines. 



The disconnected, broadly falcate, paddle-shaped pleune help 

 to distinguish this beautiful little species, which by its narrow 

 elongate form resembles a Remopleurides. One entire specimen 

 collected from the schists at Golen Goed, Myddfai, by Mr. Wil- 

 liams of Llandovery, and presented to Prof. Sedgwick by him. 



(Col. University of Cambridge.) 



Ogygia radians (M'Coy). 



Sp. Char. Py gidium nearly semicircular, slightly convex; axis 

 conical, undefined at the end, having three narrow segmental 

 furrows at the anterior end, lateral lobes with three broad ra- 

 diating ribs faintly divided at their axal ends by a small pleival 

 furrow ; margin tumid, entire. Length 4 lines, width 7 lines. 



I provisionally give this name to a small pygidium not unlike 

 that of the Barrandia Cordai, but, from the duplicate lateral fur- 

 rows, belonging more probably to Ogygia; probably confirma- 

 tory of this view I observe in the 2nd Decade of the * Geol. Surv.' 

 t. 7. f. 5. a small eight-jointed true Ogygia from Builth, having 

 the pygidium almost identical with the present species, if, as I 

 suspect, the duplicating furrows have been accidentally omitted 

 (the figure alluded to is given as the probable young of the 

 Ogygia dilatata (Phil.), a trilobite which has not been found at 

 Builth, but abounds in the schist at Waterford). 



