1894. PROCEEDINGS OF THE NATIONAL MUSEUM. 91 



Distrihuthyd. — Subtropical America, the Gnlfs of California and Mex- 

 ico in shoal quiet water varying from salt to fresh, but preferably some- 

 what brackish, as in the case of oysters; range in time from the newer 

 miocene to recent seas. 



The genus falls naturally into three sections, the typical group best 

 illustrated by G. cuneatus; a second, Miorangia, Dall, represented by 

 the miocene G. Johnsoiii, a very small, extremely inequilateral type 

 with obsolete pallial sinus and the cardinals reversed, the superior pair 

 being in the left valve; the other, named RangkmeUa by Conrad, being 

 characterized by subequal faintly rugose lateral teeth, an obsolete pal- 

 lial sinus, and a more equilateral elongate and smaller shell. 



The subgenus Rangianella forms the transition toward MiiUnia, and 

 some of its species can only be distinguished from species of Mulhiia 

 by the smaller pallial sinus and the inconspicuous "hook" on the 

 proximal end of the anterior lateral tooth. A number of small species 

 of Mtdima\\di\^ been described under the name of Rangia or Gnathodon, 

 so close is the relation between them. Several species of Mulinia^ if 

 not all of them, are denizens of brackish water, and to errors based on 

 these facts are due the statements wiiich have represented Gnathodon 

 as being extra- American in distribution. 



As far as I have been able to judge from the specimens 1 have seen, 

 the species described will be assorted as follows: 



A: Gnathodon; typical group; G. cimeatus iTTny, G. clathrodon Can- 

 rad, G. Grayl Conrad, G. Leeontei Conrad, G. minor Conrad. 



B: Miorangia', G. Johnson i DaW. 



C: Rangianella; G.fltxiiosus Conrad, 6r. ro.s-/r«f».<f Petit, G. trigonus 

 Petit, G. mendicus Gould. 



The other species hitherto described may be referred to MuUnia, 

 Isocardia, and other groups external to the genus as properly restricted. 



This genus has had singular nomenclatorial vicissitudes. The type 

 species was well known to the early conchologists of the United States, 

 and was regarded by them as identical with the jiroblematical fossil 

 named by Lamarck Cyyenatruncata. Gray, from a ballast heap left in 

 Canada by a vessel from the Gulf of Mexico, received two valves, which 

 he described under the name of (7a///ror/on, and sent the manuscript to 

 the editors of the American Journal of Science, to be published in 

 America, about 1830. Believing it to be the same as Lamarck's species, 

 the editors suppressed Gray's description. Later Gray substituted 

 Gnathodon for the ill-constructed name Clathrodon, and the former was 

 published by Sowerby in his "Genera of Mollusca," Part xxxvi. This 

 was the first publication of the name Gnathodon., and appears to have 

 been made in the last quarter of the year 1831,* the number containing 



* See Newton, Brit. Oligocene and Eocene Moll., p. 321, 1891. Since writing this 

 note the researches of Mr. C. Davies Sherborne, kindly nudertalven at my suggestion, 

 show that No. xxx\'i was received and entered ou the donation book of the Lin- 

 nean Society, Loudon, January 4, 1832; from which it may be inferred that the 

 number in question was printed in the last days of December. 1831. 



