XVIII STRATIGRAPHICAL DISTRIBUTION 507 



make their appearance, such as Stroiihomena, Lei[)taena, Atryim, 

 llhyiwlionella, CI ifamhofiites, etc., hut the extraordinary abundance 

 and variety of Orthis is most remarkable. The Ecardines are 

 reinforced by such forms as Trematis and Slplionotreta. It is, 

 however, in the Silurian that the Testicardinate Brachiopoda 

 attain their maximum, for in addition to a great development of 

 species amongst the older forms, a host of new genera for the 

 first time occur here (Sjjirifera, Atliyris, Concliidium, Stricklandia, 

 Chonctes, Cyrtia, etc.) ; and the Trimerellidae are especially 

 characteristic of the Wenlock. 



With the commencement of Devonian times many species and 

 genera l»ecome extinct, but new forms come in {Terchratula, 

 Orthothetes, Productus, etc.), and some genera are wholly confined 

 to this formation ( Uncites, Stringoccplialus). The Carboniferous is 

 marked by the maximum development of Froductus and Spirifcra; 

 Ortliothetes, Ste^iochisma, and Athyris are also abundant, but there 

 is a consideral:)le extinction of the older genera and species, and a 

 great diminution in the number of individuals and species of 

 those that persist. 



A further reduction occurs in the Permian, where the most 

 important genera are Productus, Strophalosio.., and Stenocliisma ; 

 but Aulosteges is a new form peculiar to this period. In the 

 Trias a new era commences ; the principal families and genera 

 of the older rocks disappear entirely ; a few spire-bearing genera 

 persist (Spiriferina, Athyris), and the genus Koninckina is 

 restricted to this formation. 



The enormous development of species of the Terebratididae 

 and RhynehoneUidae is the most noticeable feature in Jurassic 

 times ; and a few ancient types linger on into the Lias (^Sjnri- 

 ferina, Suessia, a sub-genus of Spirifera) ; Koninchella here occurs. 



The Cretaceous Brachiopoda are closely allied to the Jurassic ; 

 Magas and Lyra are peculiar to the period, and the Terebratulidae 

 and PhynchoneUidac are very abundant, together with the 

 Ecardinate genus Crania. 



With the commencement of Tertiary times the Brachiopoda 

 have lost their geological importance, and have dwindled down 

 into an insignificant proportion of the whole Invertebrate fauna. 



The distribution of the Brachiopoda in past time is shown 

 in the folio win 2; table : — 



