BRACmOPODA. 121 



1884. Discina, Worthen. Bulletin No. 2. Illinois State Museum Natural History. 



1884. Discina, White. Thirteenth Ann. Rept. State Geologist Imiiana. 



1884. Discina, Walcott. PaliEontolog-y Eureka District. 



1885. Discina, Clarke. Bull. No. IG, U. S. Geological Survey. 

 188S. Orbiculoidea, Herrick. Bull. Denison Univei-sity, vol. iv. 



From the lack of proper apprehension ol' the type-species of the genera 

 Discina, Orbicula and Orbiculoidea, there has long been, and .still exists great 

 confusion among authors in the application of these terms. The zealous 

 endeavors of Mr. AY. H. Dall* to unravel the complications in which these 

 genera are involved, and to clear away the uncertainty in regard to the specific 

 values of the types, ought to go far toward removing the general reluctance to dis- 

 turb the currency of some of these terms, especialh^ Discina, a name in almost 

 universal use for forms confessedly not congeneric. The rectifications required 

 in such a case as this are of so fundamental a nature as to cause a certain 

 disquietude, but such instances serve to emphasize the necessity for the enforce- 

 ment of the rule too often violated, that the application of a generic name 

 must be in harmony with the characters of the type-species. 



The genus Discina was described by Lamarck in lS19,f and the typical 

 example taken, D. ostrceoides, Lamarck, of which neither figure nor description 

 was given. It appears from observations by Reeve,! that the originsil specimen 

 used by Lamarck was obtained from Mr. J. de C. Sowerbv, and Dall observes§ 

 that it " is the same species and from the same lot of specimens, as the shell 

 described by Mr. G. B. Sowerby in the Linnean Transactions, and well figured 

 by him there under the name of Orbicula Norvegica. His very excellent figure 

 enables me to speak with positiveness in saying that it is identical with Crania 

 radiosa, Gould, of which the type-specimens are before me. The figures of 

 Schumacher are sufficiently exact to allow of identifying the species with his 

 [Schumacher's] Crania striata." But this Orbicula Norvegica of Sowebby|| is 



*Bull. Museum Comparative Zoology, Harvard College, vol. iii, No. 1. 1--71. 

 t Histoire Naturelle des Animaux sans vertebres, vol. vi, p. 236. 



I Conchologia Iconica; Mongi-. genus Orbicula. 1862. See, also, Revision of the History, Synonymy, 

 and Geographical Distribution of the recent Crania and Orljiculae, in Ann. Nat. Hist., vol. x. 1'^''2. 

 § Bull. Museum Comparative Zoology, loc. cit., p. 40. 

 1 Trans. Linnean Society, vol. xiii, ji. 46S. 1822. 



