THE FACTS 383 



tiXmida) common. The remaining 2 species are not represented by name 

 in the Wenlock limestone of this section, but their specific characteristics 

 are recognized in the fauna, as shown by the following statement : 



Dinobolus (Monomer ella) davidsoni Salter (of which Davidson re- 

 garded M. woodwardi Salter as a variety) is listed by Davidson in the 

 Shropshire section from the Wenlock limestone. The variety wood- 

 wardi is the form recognized in the Edmunds fauna. This variety (M. 

 woodwardi Salter) is reported in the Woolhope district farther south 

 from the Wenlock limestone by Salter. Wilsonia splicer oidalis McCoy is 

 regarded by Davidson as a small variety of Wilsonia wilsoni Sowerby. 

 (See British Silurian Brachiopods, page 170, where it is called Rhyn- 

 chonella wilsoni var. sphmroidalis McCoy.) In the Shropshire section 

 R. sphceroidalis is very rare in the Buildwas beds or Lower Wenlock 

 shales and common in the (Tickwood) Upper Wenlock shales and in the 

 Wenlock limestone, and Rhynchonella wilsoni is marked "common" in 

 the shales overlying the Wenlock limestone and in the Lower Ludlow, 

 Aymestry, and Upper Ludlow. In the Malvern, May Hill, and Usk dis- 

 tricts, farther south, R. wilsoni is reported by Salter from the Wenlock 

 limestone. 



Thus it appears that the 7 Brachiopods by which the Edmunds fauna 

 is distinguished from the Eochester fauna occur in the typical Wenlock 

 limestone of England, though 2 of them are restricted to its southern 

 extension. None of them, moreover, have a range downward in the. 

 Shropshire section farther than the Tickwood beds immediately under- 

 lying the Wenlock limestone except Meristina tumida, which is marked 

 "very rare" in the Lower Wenlock shales (Buildwas beds), while 1 of 

 them range upward into the Lower Ludlow, 3 into the Aymestry, and 2 

 into the Upper Ludlow of this same section. 



Again, all of them are distributed southward in the Wenlock beds of 

 the southern English and Welch districts. 



Following the Wenlock beds northward into North Wales and southern 

 Scotland, the rarity of any one of these 7 species is conspicuous. For 

 instance, the list of the Silurian fossils of the south of Scotland in the 

 collections of the Geological Survey of Great Britain 7 records from the 

 Wenlock limestone only Whitfieldia tumida and Rhynchonella wilsoni of 

 this list of 7 significant Brachiopods from the Edmunds. It includes, 

 however, the following species, which are typically Wenlock species: 

 Pholidops implicata, Cyrtia exporrecta, Plectambonites transversalis, 

 Nucliospira pisum, Bilobites biloba, Dalmanelja elegantula, Spirifer sul- 



7 Memoirs of the Geological Survey of Groat Britain, vol. 1. Scotland, 1809. 



