DEVONIAN AND OLD RED PERIOD. 149 



their allies). In all these forms there is a horny skeleton, of a 

 fan-like or funnel-shaped form, which grew attached by its 

 base to some foreign body. The frond consists of slightly- 

 diverging or nearly parallel branches, which are either united 

 by delicate cross-bars, or which bend alternately from side to 

 side, and become directly united with one another at short 

 intervals in either case giving origin to numerous oval or 

 oblong perforations, which communicate to the whole plant- 

 like colony a characteristic netted and lace-like appearance. 

 On one of its surfaces sometimes the internal, sometimes the 

 external the frond carries a number of minute chambers or 

 " cells, " which are generally borne in rows on the branches, 

 and of which each originally contained a minute animal. 



Fig. 95. Spirifera 



tculptills. Devonian, Ca- Fig. 96. Spirifera mucronata. Devonian, America, 



nada. (After Billings.) (After Billings.) 



The Brachiopods still continue to be represented in great 

 force through all the Devonian deposits, though not occurring 

 in the true Old Red Sandstone. Besides such old types as 

 Orthis, Strophomena, Lingula, Athyris, and Rhynchonella, we 

 find some entirely new ones ; whilst various types which only 

 commenced their existence in the Upper Silurian, now under- 

 go a great expansion and development. This last is especially 

 the case with the two families of the Spiriferidce and the Pro- 

 ductidce. The Spirifers, in particular, are especially character- 

 istic of the Devonian, both in the Old and New Worlds some 

 of the most typical forms, such as Spirifera mucronata (fig. 96), 

 having the shell " winged, " or with the lateral angles prolonged 

 to such an extent as to have earned for them the popular name 

 of " fossil-butterflies. " The closely-allied Spirifera disjuncta 

 occurs in Britain, France, Spain, Belgium, Germany, Russia, 

 and China. The family of the Productida commenced to exist 

 in the Upper Silurian, in the genus Chonetes; and we shall 

 hereafter find it culminating in the Carboniferous in many 



