DEVONIAN AND OLD RED PERIOD. 145 



principal forms belong to the genera Phacops (fig. 88, a, c, */), 

 Hotnalonotus (fig. 88, &}, Proetus, and Bronteus. The species 

 figured above under the name of Phacops latifrons (fig. 88, a}, 

 has an almost world-wide distribution, being found in the 

 Devonian of Britain, Belgium, France, Germany, Russia, Spain, 

 and South America ; whilst its place is taken in North Ame- 

 rica by the closely-allied Phacops rana. In addition to the 

 Trilobites, the Devonian deposits have yielded the remains of 

 a number of the minute Ostracoda, such as Entomis (" Cypri- 

 dina "), Leperditia, &c., which sometimes occur in vast num- 

 bers, as in the so-called " Cypridina Slates " of the German 

 Devonian. There are also a few forms of Phyllopods (Es- 

 theria). Taken as a whole, the Crustacean fauna of the 

 Devonian period presents many alliances with that of the 

 Upper Silurian, but has only slight relationships with that of 

 the Lower Carboniferous. 



Besides Crustaceans, we meet here for the first time with 

 the remains of air-breatJiing Articulates, in the shape of Insects. 

 So far, these have only been obtained from the Devonian 

 rocks of North America, and they indicate the existence of at 

 least four generic types, all more or less allied to the existing 

 May-flies (EpJicmeridce). One of these interesting primitive 

 insects, namely, Platephemera antiqua (fig. 89), appears to have 

 measured five inches in ex- 

 panse of wing; and another 

 (Xenoneura antiquoruni) has 

 attached to its wing the re- 

 mains of a " stridulating- 

 organ " similar to that pos- 

 sessed by the modern Grass- 

 hoppers the instrument, as 

 Principal Dawson remarks, 

 of " the first music of living 

 things that Geology as yet 

 reveals to us." 



Amongst the Mollusca, the Devonian rocks have yielded a 

 great number of the remains of Sea-mosses (Polyzoa). Some 

 of these belong to the ancient type Ptilodidya, which seems to 

 disappear here, or to the allied ClatJiropora (fig. 90), with its 

 fenestrated and reticulated fronds. We meet also with the 

 graceful and delicate stems of Ceriopora (fig. 91). 



The majority of the Devonian Polyzoa belong, however, to 

 the great and important Palaeozoic group of the Lace-corals 

 (Fcnestdla, figs. 92 and 94, Retepora, fig. 93, Polypora, and 

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



