50 



PALAEONTOLOGY 



which attain their climax inrecent seas. Five species of Argiope 

 occur in the greensand, chalk, and tertiaries. The allied genus 

 Thecidium is represented by one species in the carboniferous and 

 one in the triassic system, becomes comparatively common in the 

 secondary period, and dwindles again to a single species in the 

 newer tertiary ; this species survives within still narrower 

 limits in the Mediterranean Sea. The sub-genus Tcrebratv- 

 lina is represented by twenty species in the secondary and 



Fig. 11. 

 Brachiopoda. 



i. Trigonosemus Palissyi, Woodw. : U. Cretaceous, Ciply. 



2. Stringocephalus Burtini, Defr. ; Devonian, Eifel. 



3. Spirifera striata; Carboniferous, Britain. 



4. Cyrtia trapezoidalis ; U. Silurian, Dudley. 



5. Athyris Roissyi, Ler. ; Carboniferous, Ireland. 



6. Uncites gryplms, Schl. ; Devonian, Belgium. 



7. Atrypa reticularis, L. ; U. Silurian, Malvern. 



8. Pentamerus lrevis; Caradoc S., Salop. 



tertiary formations. T. striata of the chalk is so like the recent 

 T. ccqnd serpentis as to be with difficulty distinguished from it. 

 Several extinct sub-genera occur in the cretaceous strata, of 

 which the most remarkable are Trigonosem/us (fig. 11, 1) and 

 Lyra, shaped like a violin. The genus Stringocephalus (fig. 

 11, 2) is peculiar to the Devonian strata, and has a large 



