131 



occurs 1,000 feet below. Second he assumes that Leptobolus atavus, a 

 shell quite different in form is the young of this species. Third that 

 Lingulella tumida, a thick shelled species is also the young of Lingulepis 

 Gregwa, which is thin-shelled. How the two named can be the young of this 

 species seems difficult to understand, seeing that they occur in layers 300 

 feet above it, and that L. Gregwa does not occur in the layers with them, 

 nor they in the lower horizon with it. These errors seem the more 

 remarkable, since Mr. Walcott sent to me for these specimens for study, 

 and they were distinctly marked as belonging to the Etcheminian terrane. 



Var. ROBUSTA, n. var. 



Intermingled with the above species there are valves of a form nearly as Variety 

 large, which differs in its thicker and stiffer test, its more shining surface ro 

 and straight posterior margins of the ventral valve (not incurved as in 

 L. Gregwa). The concentric growth grooves are rare or weak in this 

 form. It is placed here as a variety until better known. 



The following table will show its relation to L. Gregwa : 

 VALVES of var. robusta from Assise E. 1 d. 



C R. 



