THE CULT OF THE TRILOBITES 6oi 



they were the dominant forms of marine Hfe, and in those ages 

 we have no trace of any superior creatures on the land. 



While the general form for a well-conducted trilobite was 

 a flattened ovoid, some of the Silurian genera show a fine 

 exuberance of style. The Ordovician ^glina has a swollen 

 head-bulge worthy of a scholar, while the Gotlandian Aci- 

 daspis bristles with spines, and Deiphon from the same system 

 has narrowed down parts that are ordinarily in contact, until 

 they stick out laterally as fantastic spikes. The Devonian 

 trilobites show a far more sober tendency ; the genera are 

 reduced in number, and in Carboniferous times very few 

 remain, descendants of early and unassuming forms. One 

 genus, Anisopyge, survives into the Permian period. 



Trilobites, then, attract by their quaintness and antiquity. 

 Their carapaces are divisible into a head-shield, a body-portion 

 (the thorax), and a tail-piece {the pygidimn), and on these a three- 

 lobed structure, running from front to back, may commonly 

 be traced. On the head-shield there is a central bulge, the 

 glabella, with a cheek on either side ; the body-portion shows 

 an axial bulge, with lateral extensions, the pleurce, at a lower 

 level on either side ; the features of the thorax are carried on to 

 the pygidium, and the axis is in many genera here prolonged 

 into a spine. The body-portion is clearly divided into segments, 

 from two to as many as forty-four, both these extremes occurring 

 in genera from the Cambrian system. Some genera could roll 

 themselves up, like woodlice, for comfort or protection. Both the 

 head-shield and the p3^gidium commonly show traces of seg- 

 mentation, as if they were originally or ancestrally flexible 

 and had been modified by fusion of their parts. P. E. Raymond, 

 however, in a stimulating paper which has been largely utilised 

 in the present article, suggests that segmentation set in from 

 an early condition when the carapace was continuous. 



Till now, it has been usually supposed that the primitive 

 form of the trilobites was segmented and worm-like, and 

 showed little differentiation from one end to the other. H. M. 

 Bernard, who devoted much thought to the matter, represented 

 the ancestor as " a richly segmented annelidan " {Quart. Journ. 

 Geol. Soc, vol. 50, p. 430, 1894). When he worked on phyllo- 

 pods under Huxley, discoveries of much importance were being 

 made in America as to the structure of certain well-preserved 

 specimens of trilobites, and of these he took full advantage 

 (see also ibid., vol. 51, p. 352), 



From that time onwards, discovery in regard to trilobites 

 has been mainly in the matter of appendages. When Hermann 

 Burmeister wrote his treatise, The Organisation of Trilobites, 

 deduced from their Living Affinities, for the Ray Society in 1846, 

 he concluded (p. 44) that " the feet of trilobites were too soft 



