F. R. Cou-per Reed — On the Phacopidce. 225 



genal angles produced into spines ; thoracic pleuree with pointed 

 ends ; pygidiiim strongly mucronate and of many segments, 12-16 \^ 

 in Silurian species, more than 16 in Devonian. Subgenus Dabnanites, 

 sens. str. { = Hausmannia). 



Division III. Highly specialised forms (e.g. Asteropyge punctata, 

 (Stein.)), with pentamerism of head sometimes distinct, sometimes 

 more or less lost by fusion of lobes ; genal angles generally spined ; 

 margin of head frequently furnished with spines or processes ; 

 thoracic pleurge pointed or produced into spines ; pygidium of many 

 segments, 16-20 or more, margin usually ornamented with many 

 spines or processes.^ The most important character in this division, 

 according to Kayser,^ is the large number of axial rings in the 

 pygidium, which here reaches the maximum in the family. The 

 members of this division include Asteropyge, Coronura, Cryphina, 

 Gorycephalus, Odontocephalus, Malladaia, and Proholium. The sub- 

 generic independence of these is open to question, and Clarke's name 

 Synphoria would include them all. 



Branch B. 



The second branch of the Phacopidse, which culminates in 

 '^PJiacops, sens, str,, branches off from the primitive division of 

 Dalmanites as above stated; and an early stage along this line is 

 found in the Ph. Glockeri group of Etage E in Bohemia, which is 

 characterised by the general shortening and widening of the 

 cranidium ; the partial loss of the pentamerism ; the weakening 

 or obliteration of some of the lateral furrows of the glabella (with 

 the frequent splitting or interruption in the course of the anterior 

 one) ; the rounding of the genal angles ; the increased convexity of 

 the thorax ; the rounded or obtuse ends of the pleuree ; the 

 comparatively few segments and the rounded non-mucronate outline 

 of the pygidium ; and the general absence of spines. In Northern 

 Europe this stage in the development of the true Phacops is 

 represented by the Silurian groups named Acaste and PortlocTciu,^ 

 which possess the above characteristics with minor modifications. 

 The third pair of lateral lobes in the glabella is the most persistent 

 and distinct of the lobes, though often tending to become nodular ; 

 and in all the features of this stage we see the beginning of 

 modifications leading up to the Devonian type ; but we cannot 

 definitely state that they are in the direct line of evolution of the 

 typical Phacops ; and the significance of their relatively small 

 size is not at present understood. However, the morphological 

 characters of the Acaste, Portlochia, and Ph. GlocTceri groups show 

 a transitional condition, and being confined to the Silurian (with 



^ Barrois has recorded from the Silurian of the Pyrenees a species Dalmanites 

 Gourdoni, possessing the short pygidium of 10-11 axial rings, like those in Div. II, 

 hut with the margin spinose (Ann. Soc. Geol. Nord, x, 1883, p. 151, pi. vi, fig. 1). 



• Kayser: Zeitschr. dent. Geol. GeselL, Ed. xxxii (1880), p. 19. 



^ Portlockia has no phylogenetic or morphological characters of sufficient value to 

 separate it subgenerically from Acaste, as Salter recognised years ago. 



DECADE v.— VOL. II. NO. Y. 15 



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