Lohlcy — Distrihution of British Brachiojpoda, 499 



Of tlie species composing these genera and sub-genera, very few 

 have a range extending through more than one or two formations, 

 while several, as Terehratula fimbria for example, characterise a par- 

 ticular zone or stratum of, in some instances, not more than a few 

 inches in thickness. The elaborate works of Dr. Davidson, however, 

 give with so much minuteness the range of particular species that I 

 will pass on to a brief consideration of the range and distribution of 

 the genera and sub-genera. 



The oldest of all the Brachiopods is the Lingulella — L. ferrugmea 

 having been found by Dr. Hicks in Cambrian rocks. This genus 

 ranges through the Primordial Silurian group, giving name to the 

 Lingula flags, in which Lingulella Davisii is exceedingly abundant. 

 Above the Tremadoc slates, Lingulella has not, with certainty, been 

 found. Obolella having recently been found in the Upper Longmynd 

 rocks, must be placed next. This genus, like Lingulella, attains its 

 maximum development in the Primordial Silurian ; and dies out in the 

 Llandeilo rocks, in which only one species has hitherto been discovered. 



A Discina has, it is said, been also found in older rocks than any 

 ha^'ing a right to a place in the Primordial Silurian, and therefore 

 that genus is entitled to the third place. Discina, however, has a 

 much greater range than the two previously mentioned genera, since 

 it is found in Palseozoic, Mesozoic, and in Cainozoic strata, and is, 

 moreover, a living genus at the present day, though it has been 

 searched for in vain in many formations both in the Paleeozoic and 

 Mesozoic groups. The greatest number of species of Discina have 

 been taken from Caradoc strata, though not more than five well- 

 marked species have been discovered in these rocks. 



The very important genus Ortliis is represented by no less than 

 30 species in the Caradoc rocks, but its range has not been found to 

 extend further than from the Primordial Silurian to the Carboniferous 

 Limestone. 



Lingula, of which Lingulella may be termed perhaps rather a sub- 

 genus than considered a separate genus, appears next, and has a 

 range from the Primordial Silurian to the latest formations, and lives 

 in the present seas of the world. It is not, however, in any forma- 

 tion represented by many species, and in not any of the Mesozoic or 

 Cainozoic rocks do we find more than one species. The genus 

 attained its maximum development in the Llandeilo rocks, in which 

 eight species have been discovered. 



Crania will be seen to have a very long range, but it is represented 

 by very few species. 



The important genus Bhynchonella commences in the Caradoc and 

 ranges to the present time, JR. psittacea being found living in the 

 Northern seas. It is largely represented in Silurian, Devonian, 

 Carboniferous, Oolitic, and Cretaceous rocks, but only one species 

 has been found in Tertiary strata. 



Spirifera, the next genus, has its maximum number of species in 

 Carboniferous rocks, in which we find no fewer than 27 well-marked 

 species. Mr. C. Moore has discovered two species in the Inferior 

 Oolite, in which this genus appears to have died out. 



