4 



BRITISH FOSSILS. 



female of that species, a rudimentary spine or tubercle is all that 

 occurs. Several others are described, S. armata, &c., distinguished 

 by such an appendage ; it may perhaps be proved that some of these 

 are males of the unarmed species. 



Affinities, - As nearly all the known species are double the size 

 of this, a close comparison is not necessary ; and Cyphaspis Bur- 

 meisteri, Barr., besides its very much larger size, has 7 to 15 

 thorax rings according to its age, and the tail with five rings to 

 the axis ; the space, too, between the glabella and front margin is 

 very wide : the posterior head spines short, reaching only to the 

 4th ring. Like our species, it bears a spine on the 6th thoracic 

 segment. G. Barrandei, Corda (the species called formerly, with 

 doubt, G. clavifrons, by Barrande) has 11 rings, but the glabella is 

 vastly more inflated and the head margin narrow ; the posterior 

 head spines, too, are one and a half times the length of the body. 

 G. cerherus, of the same author, has the head fringed with spines ; 

 and the Devonian species, G. ceratophthalma, Goldf, besides its 

 greater bulk and much more convex head, has a scrobicula or pit at 

 each of the posterior head angles. The pretty Swedish species, 

 G. elegantulus (Proetus eleg., Angelin), is more like ours, but has an 

 elongate head and 12 unarmed thorax rings. In fact there is no 

 published fossil which can be confounded with it. 



The genus is more rich in species than might be supposed, but 

 they have only been discovered of late years. G. ceratophthalma, 

 Goldf, of the Eifel, furnished Professor Burmeister with the type, 

 which he described in 1842, in his original work ; since which time 

 Barrande, Lov^n, and Sandberger have made us acquainted each 

 with a few species. M. Corda has largely swelled the list, divid- 

 ing the genus into Goniopleura, with 12 rings, Gyphaspis, with 

 11, and Gonoparia, with 13 ; but the diflerences he notices are 

 by no means sufiicient for the establishment of distinct genera, 

 though possibly the species with a very wide space in front of the 

 glabella, and with more than 11 body rings, may form a sub- 

 genus. Now that we possess the work of M. Barrande, who has 

 discovered the several species with great variations in the number 

 of thorax rings according to their age, (in G. Burmeisteri, from 

 7 to 15), the limits of these sub-genera may perhaps be arrived at. 

 Our species, at all events, will fall into the same group of 11-ringed 

 species, with that originally described by Burmeister. 



History. — Abundant but very imperfect specimens of the head 

 of this little trilobite were detected by Professor M'Coy, and 

 carefully described by him in his account of the Irish Silurian 



