BRACHIOPODA. 249 



tlie genus equivalent to Orthothetes, of Fischer de Waldheim, 1837, as now 

 defined. 



In his "Monograph of the Permian Fossils of England " (1850, p. 103), 

 Professor King, under the head of ''Family Strophomenw^, King, 1846," writes 

 as follows : 



" Rafinesque was the first to found a genus for shells belonging to this family. 

 Whether his Strophomena were ever published by himself, or it first appeared 

 under the editorship of some other author, I have not been able to ascertain ; 

 but this is certain, that the genus was described by M. de Blainville, in his 

 ' Manuel de Malacologie,' 1825, and afterwards in the ' Dictionnaire des 

 Sciences Naturelles,' t. li, 1827, in both of which it is typified by the American 

 Strophomena rugosa, Raf., which, from its general form, and its large valve 

 being concave, and the opposite one convex, 1 have little doubt is identical 

 with the recently proposed Strophomena (Leptana) planumbona, of Hall.*" 



But King also included in the genus " such shells as S. alternata, Conrad, 

 S. Dutertrii, Murchison, S. euglypha, Dalman, S. planoconvexa, Hall, and several 

 others"; a group in which are now recognized three distinct generic types 

 of adult characters In 1853, f Mr. Davidson followed Professor King in 

 assuming as the type " S. riigosa, Raf. ? = S. pJanumbona or S. alternata'' 

 This conception of the value of the genus Mr. Davidson did not modify 

 in any. of his subsequent writings, except in his last reference to it, in 

 the "General Summary" of 1884. The reversal of the relative convexity 

 of the valves in the above species, which was indicated in Defrance's 

 description of S. rugosa, and which is now regarded as an important mor- 

 phological character, was not regarded by Mr. Davidson as of high value. The 

 fact that the reversed species have, in early growth- stages, the normal convexity 

 which is retained throughout by such forms as S. alternata, was considered as 

 evidence of homogenity ; hence he included in this genus " all species agreeing 

 with S. planumbona, alternata, grandis, filosa, euglypha, fmiculata, antiquata, peden, 

 expansa, depressa, etc.," although in this list are species with normal convexity 



* " Vide Palffiontolngy of New York, vol. i, p. 112, pi. xxxi b, fig. 4 ; and Bull, de la Sac. Geo!, de France, 

 2me seiie, t. v, pi. iv, figs. 3 a, b, c, d." 



t Introduction British Fossil Brachiopoda, p. 105. 



