436 



FOSSILS OF THE WENLOCK LIMESTONE. [Ch. XXVIl 



tioned (p. 403), exhibitiDg the quadripartite arrangement of tlie lamellae 

 within the cup. 



Among the numerous Crinoids, several peculiar species of Cijathocrinus 

 (for genus, see figs. p. 405) contribute their calcareous stems, arms, and 

 cups towards the composition of the Wenlock limestone. Of Cystideans 

 there are a few very remarkable forms, some of them peculiar to the 

 Upper Silurian formation, as for example the Pseudocrinites, which was 

 furnished with pinnated fixed arms,^ as represented in the annexed fig- 

 ure (fig. 582). 



The Brachiopoda are for the most part of the same species as those of 

 the Aymestry limestone; as, for example, Ahypa reticularis (fig. 575, 

 p. 434), and StropJiomena depressa^ Sow. sp. (fig. 583) ; but these species 

 range also through the Ludlow rocks, Wenlock shale, and Caradoc 

 Sandstone. 



Fig. 582. 



Fig. 5S3. 



Strojplwmena {LejytoRna) deprenm^ Sow. 

 "Wenlock and Ludlow Eocks. 



Pseudocrinites Mfaseiatus, Pearce. 

 "Wenlock limestone, Dudley. 



The Crustaceans are represented almost exclusively by Trilobites, which 

 are very conspicuous. The Calymene Blumenbackii, called the " Dudley 

 Trilobite," was known to collectors long before its ti^ue place in the animal 

 kingdom was ascertained. It is often found coiled up like the common 

 Oniscus or wood-louse, and this is so common a circumstance among the 

 trilobites as to lead us to conclude that they must have habitually resorted 

 to this mode of protecting themselves when alarmed. Sphcsrexochus 



Fig. 585. 



Fig. 584 



Calymene Blumen'bacMi, 



Brong. 



"Wenlock, Ludlow, and 



Aymestry limestones. 



Fig. 586. 



SpJicerexoelius miru.% Bey- 

 rich. Coiled up. 

 Dudley; also in Ohio, 

 N. America. 



Phacops eaudaiuff, Brong. 

 "Wenlock, Aymestry, and Ludlow Eocks, 



* E. Forbes, Mem. Geol. Survey, vol. ii. p. 49&. 



