F. R. Cou'ijer Reed — On the Phacopidw. 177 



and its characters are, as we should anticipate, somewhat composite 

 and varied. The elements of future lines of development are found 

 to be contained within its limits. For example, the genal angles 

 are sometimes spined and sometimes rounded ; the same is the case 

 with the extremities of the thoracic pleuras ; the pygidium, though 

 always consisting of fewer segments than in the Dalmanites of later 

 periods, is in some species elongated and mucronate, while in others 

 it is rounded and has a simple margin. Two sub-groups can in fact 

 be distinguished in the Bohemian group of primitive Dalmanites, 

 as Hoernes has pointed out : one sub-group marked by D. Angelini 

 and D. socialis, leading onward into the typical Silurian Dalmanites, 

 while the other, which comprises such forms as D. atavus and 

 D. Phillipsi, has more in common with the later group of Fh. Glockeri. 



Branch A. 



In the case of the branch culminating in the spinose and otherwise 

 ornamented representatives of Dalmanites of the Devonian period, 

 there is no continuous chain of forms in Bohemia connecting the 

 latest developments of the pentamerous series with the early stock. 

 Etage E affords no evidence of the existence of this branch, and 

 perhaps the scene of its evolution was temporarily moved elsewhere. 

 In Northern Europe, and even in the British Isles alone, we are able 

 to fill up this gap to some extent. For in England, succeeding the 

 Arenig forms of early Dalmanites, we get a variety of D. socialis in 

 the OrtJiis argentea shales of South Wales,^ and in the Sholeshook 

 and Redhill Beds we find D. Robertsi,^ in which the characters are 

 composite as in the Bohemian early stock. Then comes D. appendieii- 

 latus, Salter, of the Bala and Ashgill shales, possessing most of the 

 features of a typical Silurian Dalmanites, though it has fewer 

 segments in the pygidium. The Silurian formation follows with 

 the type-species of Dalmanites, D. caudatus, and it is accompanied 

 by numerous allied forms, D. longicaudatus, D. Weaveri, D. obtiisi- 

 caudafus, etc. During the equivalent period in Bohemia there 

 seems to have been a complete absence of Phacopidte belonging to 

 the Dalmanites-hvanch. Passing to Scandinavia, we find the 

 Ordovician D. mucronatus (which is closely allied to the English 

 D. appendiculatus) succeeded by D. caudatus and related species. 

 The jDa/maju7es-group is also well represented in North America 

 and in Australia in Silurian beds, and has recently been discovered 

 in Burma. In the following Devonian period we meet with a great 

 and varied development of this group. In most parts of Europe the 

 spinose group of Asteropyge occurs, and less commonly the smaller 

 groups named Malladaia, CrypJiina, and Proholium. In Bohemia 

 the Devonian representatives of Dalmanites resemble structurally 

 the typical Silurian forms of other parts of Europe, except in an 

 increased number of pygidial segments. The other groups seem in 

 this part of Europe to be absent. A notable departure from the 



1 Reed: Geol. Mag., Dec. V, Vol. I (1904), p. 383, PI. XII, Fig. 2. 



2 Ibid., p. 106, PL V. 



DECADE T. — VOL. II. NO. IV. 12 



