86 GUIDE TO THE FOSSIL INVEETEBEATE ANIMALS. 



Gallery Tremadoc Slates is the usual text-book instance of how 

 VIII. fossils may be distorted by earth-movements. The Lower 

 Cambrian Hollybush Sandstone of Comley, Shropshire, has 

 yielded fragments referred to the wide-spread genus Olenelhcs. 

 Trinucleus, with its ornamented head-shield, is a character- 

 istic Ordovician genus. Asaphus tyr annus and Ogygia Buchi 

 are common in the Llandeilo Flags of the same Epoch. 

 Illaemis, with its smooth head-shield and pygidium, has 

 even lost the axal furrows from the thorax, and forms 

 a strong contrast to the spiny Acidaspis or the tuberculate 

 Encrinnrns of Wenlockian age. Galymmene Blumenhachi 

 is " the Dudley Trilobite," and to its coiled individuals is 

 due the name of the genus (" covered up "). Homcdo7iotns 

 is another form devoid of ornament and losing its furrows. 

 In Sphaerexochns, Deiphon, and Stanrocephalns (Fig. 40 c), 

 the swollen glabella is a remarkable feature. Among 

 Devonian trilobites note the fan-shaped pygidia of Bronteus 

 and the tripartite head of Trimeroceplialus. The three 

 Carboniferous genera G-rifflthides, Phillipsia, and Bracliy- 

 metopus are well represented. 

 Between In the foreign collection one may notice slabs from the 

 Wall-eases Cambrian of China covered with ''petrified swallows," as 

 "Wb^-c^sq Chinese call these remains of Steplianocare, Drepanura, 

 14. and Agnostus (Plate V). Here are fragments and a restora- 

 tion of the huge Asaphics megistos from the Ordovician of 

 Ohio. The Bohemian collection obtained from J. Barrande 

 is particularly valuable. Among the Cambrian genera one 

 • should note Ptychoparia and Sao; among the Ordovician, 

 Olenus (Fig. 40 h), Isotelus, the large-eyed Aeglina, the deeply 

 incised pygidia of Areia, and Calymmene Tristani which 

 marks a horizon of Llandeilian age. Galymmene senaria is 

 the species in which Walcott discovered the appendages 

 by means of cross-sections. Of Silurian genera, Proetus, 

 AretJmsina and Har^pes, from Bohemia, should be noticed. 

 The Devonian series includes large pygidia of Bronteus from 

 Bohemia, and several trilobites from South Africa. 



Class ARACHNIDA. 



Table-cases In this Class, as already explained, we include the 

 24 & 23. MEROSTOMATA. First in this division comes the Order 

 ^3^&°14^^ Eurypterida, whose structure may best be studied in the 

 exhibited models of Enrypterus and Hughmilleria, as well as 



