72 LIFE ON THE EARTH. 



what sense a system of life restricted to these few 

 and mostly small elements can be regarded as the 

 ancestral type of the races now living in the sea, 



gentis cunabula nostrse, 



will perhaps appear as we proceed. Lingula is 

 henceforward always present in every great group of 

 strata till we reach the Tertiaries. 



The next combination which attracts attention 

 occurs in the superincumbent group of strata, called 

 the Llandeilo formation. The following summary will 

 be sufficient for our purpose : 



Zoophyta 4 genera 4 species. 



The classes of Invertebrata are now augmented 

 to eleven : the new classes, all Molluscous, marked by 

 the asterisk, being very poor in species, while the pre- 

 viously existing classes have become much more fertile. 



The Annelida include both Cephalobranchiate and 

 Dorsibranchiate tribes. 



