50 PALEONTOLOGY OF NEW YORK. 



by the pedicle-valve of the earlier species of Lingulops (L. Whitfieldi, L. 

 Norwoodi). 



The brachial valve of this genus, with its little platform well defined, indi- 

 cates a peculiar phase of accelerated development over its companion, and this 

 same relation is manifested in L. Granti, which has the platforms developed in 

 both valves, and also in Ltngulasma, in both of which the brachial platform is 

 the larger. The same feature occui's to some extent in the other genera. 



It therefore appears probable that the inception of the platform is due to the 

 slight variation indicated in the mode or rate of formation of the muscular 

 fulcra in Lingula, and this may itself have l^een due, in part, to a simple in- 

 crease in the size of the muscular bands. 



In Lingulops Whitfieldi, the development of the platform of the brachial valve 

 is not so fixr advanced as it appears in the other species of the genus; never- 

 theless, its surface is divided by a longitudinal depression, its anterior edge 

 distinctly elevated, and its anterior wall slightly concave. In L. Norwoodi the 

 brachial platform, in its relative proportions, is almost a miniature of that in 

 Trimekella, being elongated, narrow, and divided for its entire length by a 

 median depression, but not hollow, though with its anterior walls more concave 

 or excavated than in its congener ; and in L. Granti, of the Niagara fauna, 

 essentially similar characters are manifested. 



Another consideration concerning the origin of the platform is suggested by 

 the chronological order of appearance of these fossils. The forms which have 

 been just considered, and which indicate the line of derivation from Lingula to 

 Trimerella (the latter genus being assumed to represent the climacteric develop- 

 ment of the platform), are the predecessors of Tkimerella, Monomerella and 

 Rhinobolus ; not remotely from a faunal standpoint, but actually, by a great lapse 

 of time ; the former are from the Hudson group, the latter from the Niagara 

 faunas. Ltngulops, strangely enough, has spanned this great interval, reappear- 

 ing in the Niagara fauna with some important modifications, viz., the develop- 

 ment of the muscular area of the pedicle-valve into a well-defined platform ; 

 possibly, also, the obliteration of the arched posterior scars. And Dinobolus, 

 though attaining a culmination of development with its allies in the Niagara 



