474 Mr. A. J. Jukes-Browne on the Shells 



the binge in Totten's own words, by Hanley in 1843 *, who 

 does the same, and by Sowerby in 1852 f. 



In 1853, however, Deshayes separated it as a new genus 

 under the name of Gemma, and printed a Latin description 

 of the generic characters in his c Catalogue of the (Jonchifera 

 in the British Museum,' p. 112. At the same time he refers 

 to the ' Proceedings of the Zoological Society ' for 1853 as if 

 they contained a previous description of the genus Gemma ; 

 but no such notice is to be found in that publication. In his 

 description Deshayes distinctly states that there are " dentes 

 cardinales ties in valva sinistra .... duo in valva dextra, 

 divergentes, fossula lata interposita " ; but how he came to 

 make such a mistake is a mystery, for the right valve of 

 Gemma shows three widely divergent teeth, the central one 

 being prominent and bifid. In the left valve there are two 

 conspicuous teeth with a wide space between them, but there 

 is also a narrow inconspicuous posterior tooth below the 

 ligament, which is sometimes nearly obsolete, so that it is 

 possible that Deshayes wrote " right " for left valve. 



The Messrs. Adams, in 1857, adopted Deshayes's genus, 

 and gave an English translation of his Latin description, 

 thus merely repeating his error J. It is again repeated in 

 French by P. Fischer §, although he places Gemma as a 

 subgenus of Venus. 



It was not till 1902 that this mistake was corrected by 

 Dr. Dall [|, who maintains the accuracy of Totten's original 

 description, so far as it goes, and gives a full account of the 

 different names which have been bestowed on the shell and its 

 varieties. Dr. Dall accepts Gemma as a genus, and prints a 

 fresh description of the hinge, the cardinal teeth being 

 correctly described ; but he asserts that there are also lateral 

 teeth — an anterior lateral in the right valve and a posterior 

 lateral in the left. Curiously enough, however, he describes 

 the opposite margins as " deeply grooved " to receive these 

 " lateral teeth," and does not seem to regard the inner borders 

 of these grooves as lateral teeth, though, according to all 

 precedent, he should do so. 



So far as the facts are concerned, i. e. the existence of the 

 ridged margins and the corresponding grooves, Dr. Dall is 

 quite correct, but as regards the interpretation of the facts I 

 completely differ from him. If these ridges were lateral 



* ' Catalogue of Recent Bivalve Shells,' p. 128. 



f ' Thesaurus Conchyliorum,' Moil. Ve?ius, p. 737. 



\ 'The Genera of Recent Mollusca,' vol. ii. p. 419 (issued 1807). 



§ 'Manuel de Conchyliologie,' L887, p. 1083. 



|| ' The Journal of Conchology ' (Conch. Sue. Gt. Brit.), 1902, p. 238. 



