BRACHYMETOPUS. 47 



Pygidium consisting of a variable number of segments, from ten to seventeen 

 according to the species, the axis tapering rapidly to a bluntly-rounded extremity, 

 each segment of axis ornamented with bead-like granulations, ribs with a double 

 furrow extending nearly to the border which is smooth and rounded. 



The first specimen of this genus was obtained by Mr. Frederick M'Coy, 

 from the Carboniferous Limestone of Kildare and transmitted to Portlock, who, 

 whilst struck by its dissimilarity to other Mountain Limestone forms, with which 

 he was familiar, placed it provisionally in the genus Phillvpsia, and described it 

 as Phillvpsia Maccoyi (see his ' Geology of Londonderry,' &c, 1843, p. 309, pi. 

 xi, fig. 6). 



It was left to Prof. M'Coy, in 1847, to propose a new genus for this and two 

 other species, one of which is from Australia. 



We append Prof. M'Coy's original description of the genus, from the ' Annals 

 and Magazine of Natural History,' 1847, vol. xx, p. 230. 



" Brachymetopus (M'Coy), new genus, 1847 (Etym. |3paywc, short, and fitTwirov, 

 the forehead or glabella). 



"Gen. Char. — Cephalothorax truncato-orbicular ; limb (free-cheek) narrow, 

 produced backwards into flattened spines ; glabella smooth, cylindrical or ovate, 

 about twice as long as wide, not reaching within about its own diameter of the front 

 margin ; one pair of small, basal, cephalothoracic furrows, or none. Eyes reni- 

 form, in the midst of the cheek (? smooth) ; eye-line unknown. Surface strongly 

 granulated ; one tubercle on each side of the anterior end of the glabella, the 

 marginal row and a circle round each eye being larger than the rest. Body- 

 segments unknown. Pygidium nearly resembling the cephalothorax in size and 

 form, rather more pointed, strongly trilobed, and with a thickened prominent 

 margin ; axal lobe about as wide as the lateral lobes, of about seventeen narrow 

 segments ; lateral segments about seven, divided from their origin, each terminat- 

 ing in a large tubercle at the margin. 



" The minute Trilobites for which I propose the present genus are very distinct 

 in habit from those of other genera, and as two or three species are now known, it 

 seems desirable to place them together under one name. They are the smallest 

 perfect Trilobites known, from two to three lines being the greatest width they have 

 been seen to attain. Phillipsia Maccoyi of Captain Portlock' s ' Geol. Report on 

 Londonderry,' &c, certainly belongs to this genus, and is at first sight difficult to 

 distinguish specifically from the Australian species. The Irish species alluded to 

 was collected by the writer from the Lower Carboniferous Limestone of Kildare, 

 and sent to Captain Portlock for his ' Monograph of Irish Trilobites,' under the 

 impression that it formed the type of a new genus and species, but probably from 

 there being but one specimen it was placed provisionally by that author in his 

 genus Phillipsia, from which it differs in its small, short glabella, smooth eyes, 



7 



