56 CARBONIFEROUS TRILOBITES. 



A third specimen described by Prof. Meek as Phillipsia Lodiensis (' Palaeontology 

 of Ohio,' vol. ii) should, he thinks (op. cit. p. 324), be called Proetus Lodiensis 

 (the figure, however, is unsatisfactory). 



There seems, therefore, no reason to doubt that the genus Proetus, hitherto 

 known here only in the Silurian and Devonian, may have extended upwards into 

 our Lower- Carboniferous series, as we find it on the American Continent. 



It is important also that we should bear in mind the close family relationship 

 which exists between Phillipsia, Griffithides, and Proetus ; Brachymetopus alone 

 enjoying any strongly-marked distinctive generic peculiarities. 



The general form of the body is oval ; and the trilobation very distinct through 

 the entire length of body. The head is less than a third of the total length ; 

 the pygidium is rather longer than the head; the head-shield is always sur- 

 rounded by a border, consisting of an exterior raised rim and an inner groove 

 or furrow ; the border is sometimes prolonged into a spine at the angle of 

 the free-cheeks. The posterior margin of the head is formed by the grooved and 

 furrowed border of the free-cheeks on each side and by the two basal lobes and 

 the neck-lobe, which are separated from the glabella by a very distinct and deep 

 furrow ; the neck-lobe is broader than the free thoracic somites which follow it ; 

 the glabella is usually rounded and gibbous in front, but does not overhang its 

 anterior border. (Barrande states that there are three pairs of short lateral 

 grooves on its surface, although not always to be distinguished.) The axal 

 furrows which surround the glabella are very distinct; the facial suture (which 

 divides the fixed-cheek from the free-cheek) crosses the frontal border just in a 

 line with the compound eye, above which it expands, forming a rounded palpebral 

 lobe ; then, passing down close to the line of the axal furrow, it diverges outwards 

 and crosses the posterior border obliquely behind the line of the orbit. The free- 

 cheek is triangular, its surface is convex, and upon the highest point is placed the 

 large compound reniform eye, which either sometimes exhibits a faceted surface or 

 is quite smooth, according to the state of its conservation. 



Free thoracic segments, varying from eight to ten {Proetus Barrandii, Roemer, 

 Devonian, Harz, has eight somites ; nine and ten is the common number for the 

 Silurian species). The axis is always strongly arched, and does not exceed the 

 pleurae in breadth ; the breadth of the axis diminishes very gradually to the 

 posterior extremity ; the pleurae are more or less bent at the fulcral point, and 

 have their extremities either pointed or rounded, and their anterior margin 

 faceted for rolling up. 



The pygidium varies in its elevation, but the axis is always raised above the 

 margin, and diminishes to a blunt extremity, leaving a smooth border beyond ; 

 the number of coalesced segments in the tail-shield varies (Barrande says from 



