558 



FOSSILS OF THE WENLOCK LIMESTONE. [On. XXVII. 



like that here figured (fig. 632). Another common form in the Wen- 

 lock limestone is the Omphyma (fig. 633), which, like many of its 

 companions, reminds us of some modern cup-corals, but all the Silurian 

 genera belong to the palaeozoic type before mentioned (p. 515), ex- 

 hibiting the quadripartite arrangement of the lamellae within the cup. 



Among the numerous Crinoids, several peculiar species of Cyatho- 

 crinus (for genus, see figs., p. 517) 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 Pseudo- 

 crinites, which was furnished with pinnated fixed arms,* as represented 

 in the annexed figure (fig. 633). 



The Brachiopoda are, many of them, of the same species as those 

 of the Aymestry limestone ; as, for example, Atrypa reticularis (fig. 627, 

 p. 554), and Strophomena depressa, Sow., sp. (fig, 635) ; but the latter 



Fig. 634. 



Fig. 635. 



IStropliomena (Leplcena) depressa, Sow. 

 Wenlock and Ludlow Bocks. 



Pseudocrinites difasciaitis, Pearce. 

 Wenlock Limestone, Dudley. 



species range also from the Ludlow rocks, "Wenlock shale, and to the 

 Caradoc Sandstone. There are some species, however, peculiar to the 

 Upper Wenlock, of the genera Rhynchonella Petsia, Spirifer, Athy- 

 ris, &c. 



The Crustaceans are represented almost exclusively by Trilobites, 

 which are very conspicuous. The Calymene Blumenbachii, called the 

 " Dudley Trilobite," was known to collectors long before its true 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. The other common species is the Phacops caudatus 

 (Asaphus caudatus), Brong. (see fig. 637), and this is conspicuous for 

 its large size and flattened form. Sphcerexoclius mirus (fig. 638) is 

 almost a globe when rolled up, the forehead of this species being ex- 

 tremely inflated. The Homalonotus, a form of Trilobite in which the 



* E. Forbes, Mem. Geol. Survey, vol. ii. p. 496. 



