PICTURESQUE SKETCHES 



Fig. 35 



shells of this group are not by any means strictly 

 confined in locality or limited in its range, and, with 

 the exception of the terebratula, they are perhaps 

 the most widely distributed of the fossils of the first 

 epoch. Several species pass likewise into the lower 

 beds of the middle epoch ; and it is not unlikely that 

 some of the species referred to terebratula, and now 

 living, may ultimately be recognized as spirifers. 

 The species of terebratula of the mountain limestone 

 (fig. 35) are not very strongly 

 marked, and some of them 

 are capable of misleading the 

 young fossilist by their great re- 

 semblance to shells of a much 

 newer period. The species 

 figured admits of a singular 

 extent of variety of form. 



There are many other bi- 

 valve shells of the carbonife- 

 rous limestone, and some of 

 them are of considerable in- 

 TEREBRATULA HASTATA. terest, but I cannot here venture 

 upon any detailed account of them. On the whole, 

 there is a manifest approach to the existing type, al- 

 though many genera at that time existed, all the spe- 

 cies of which have since vanished, and a much greater 

 number of new genera have been since introduced. 



Of univalve shells there are several which seem to 

 have been either chiefly or entirely confined to the 

 rocks of the carboniferous period. The name Belle- 

 ropJion * (fig. 36, 37) has been given to one genus 



* Betteroplion, a Greek narte of a person supposed to have lived in 

 the heroic age. As applied to the fossil, this name is entirely fanciful. 



