502 LoUey — Distribution of British Brachiopoda, 



If it be admitted that a Discina has been found in Cambrian 

 strata, the range of the family of Discinidce will be similar to that 

 of LinyuUdce, since we find the genus Discina living in both the 

 Atlantic and Pacific Oceans. This family is also represented by 

 very few species in any formation, the maximum number being six 

 in the Wenlock rocks. 



The CraniadcB are even more sparingly represented than either 

 the Lingididce or Discinid^ (there being only one genus), and 

 they appear in a much smaller number of formations. 



BhynchonelUdcE first appear in the Caradoc strata, represented by 

 the typical genus Bhynchonella, and only one species. In the Llan- 

 dovery strata, however, it is a much more important family ; for in 

 these rocks we find four genera and twenty species to represent 

 it. In the Wenlock rocks the same number of genera and 

 nineteen species have been found ; but when we examine Lud.low 

 strata, we only find two genera and seven species of Rhynchonellidce. 

 This important family is largely represented in the Devonian rocks, 

 — the Middle Devonian especially, which has yielded three genera 

 and eighteen species. The Upper Devonian beds do not contain 

 more than four species, but in the Carboniferous rocks we have 

 sixteen species. Three species have been taken from Permian rocks, 

 above which all the generic forms except Bhynclionella are absent. 

 The greatest number of genera of BhynclionellidcB is to be found in the 

 Llandovery and Wenlock rocks, but the greatest number of species in 

 the Inferior Oolite, in which the typical genus Bhynchonella obtains 

 a great development. 



The family of TerehratuUdoe is a very important one ; not only 

 from the abundance of the typical form Terebratida in many rocks, 

 but also from the great number and interesting character of the 

 genera into which the family has been divided. No less than twelve 

 genera and sub-genera of British fossil Brachiopoda have been 

 described as belonging to this family. Of these genera only three, 

 Terehratula, String ocephalus, and Bensseloeria, are Palasozoic ; Stringo- 

 cephalus and Bensselceria being confined to the Middle Devonian, in 

 which also the typical form Terehratula first. makes its appearance. 

 Six genera, Terehratula, Zellania, Waldheimia, Terehratella, Terebra- 

 tulina, and Argiope appear in the Lower Mesozoic rocks, the greater 

 number of generic forms of Terehratulidce being found in Cretaceous 

 strata ; and in these rocks no less than nine genera have been dis- 

 covered. We thus have the greatest number of genera of Tere- 

 hrattdidcc in Cretaceous rocks ; but the greatest number of species in 

 the Inferior Oolite, in which twenty-two species have been found. 

 Terehratulidce is very weakly represented in Cainozoic strata ; Tere- 

 hratula, Terebratidina, and Argiope, only having been discovered. 

 These genera, with three others, Terehratella, Waldheimia, and 

 Megerlia, existing in the present seas, 



When we consider the range, distribution, increment, decrement, 

 and maximum development of the class without reference to its 

 separate genera or families, we find that the class Brachiopoda is 

 represented in British strata by a very large number of species, some 

 of wliich are foimd in almost every geological formation. Coming 



