92 LIFE ON THE EARTH. 



smooth or slightly striated valves, accuminated at the 

 beaks. The shells of Terebratulse of every age ma- 

 nifest the beautiful punctation to which Dr Carpen- 

 ter called attention, and are usually smooth; while, 

 in marked contrast with its associate through the 

 immensity of time, Rhynchonella is deficient of this 

 punctation, and is commonly ridged in radiating 

 folds. 



If we place before us a series of Lingulse accord- 

 ing to their antiquity, and include the recent species, 

 we remark the absence of the genus from the British 

 Tertiaries, and the abundance of it in Palaeozoic 

 ages, the greater comparative breadth of some of 

 the older species (Lingula Davisii, L. granulata), the 

 more elliptical contour of particular examples (L. 

 elliptica from the Carboniferous rocks, L. Beanii 

 from the Inferior Oolite), but upon the whole a uni- 

 formity from one end of the series to the other, 

 which suggests very strongly the idea of very narrow 

 limits imposed on the tendency to variety in this 

 genus of mollusks. 



If we take in like manner a series of Terebratulse, 

 such as T. hastata, from the oldest known forms in 

 Devonian and Carboniferous rocks, T. elongata of 

 the Permian, T. punctata of the Lias, T. ornitho- 

 cephala of the Inferior Oolite and Fullers' Earth 

 Rocks, and T. digona of the Great Oolite, or another 



