402 Testacella maiigei {Fcr.) and T. haliotidea {Drap.). 



of Favanne himself, that it was the common species of France, 

 that is to say, the form usually known as T . haliotidea Drap., 

 and a study of Favanne's figures tends to confirm this con- 

 clusion. On the other hand, there can be little doubt that the 

 Teneriffe species, ' ex D. Mauger,' for which Lamarck sug- 

 gested the name haliotoides , is the one that Ferussac named 

 T. maugei, the only species known to occur in the Island of 

 Teneriffe. It thus differs from all of Favanne's ' Limaces a 

 Coquilles,' which Lamarck also indicated as belonging to his 

 genus. 



It is thus clear that the genus Testacella was established 

 by Lamarck for more than one species. The fact that he 

 only names a single example of the genus is no evidence to 

 the contrary, for it was his usual custom, only to mention one 

 example of each genus described in his ' Systeme des Animaux 

 sans Vertebras,' however many species it might contain. But 

 it was also Lamarck's custom to cite after the name of each 

 example any figures of that species he knew of, which had been 

 published ; and as he does not cite any of Favanne's figures 

 after his example of Testacella, but only refers to them in 

 connexion with his generic description, it seems probable 

 that he realised that the members of the genus depicted by 

 Favanne differed from Mange's species. Now, when a genus 

 is established for more than one original species, it cannot be 

 reasonably maintained that the generic description will 

 suffice instead of a specific description of any one example of 

 that genus ; for obviously the generic description should 

 apply equally to all the species included therein. Therefore, 

 since Lamarck gave no specific description or figure of his 

 T. haliotoides, his name is rightly regarded as a nomen nudum. 



The name Testacella haliotoides was next used by Bosc in 

 1802 [Hist. Nat. Coquilles, Vol. III., p. 240), and de Roissy 

 in 1805 {Hist. Nat. Moll., Vol. V., p. 253), but both these 

 authors applied this name to Favanne's first species, which, 

 as we have seen, is the form known as T. haliotidea Drap., the 

 commonest species in France. Their figures and descriptions 

 seem to be based entirely on those of Favanne, whose work 

 they cite. Yet both writers erroneously believed that this was 

 the species which Mauge found in Teneriffe, and de Roissy 

 even proposed another name for the French form. 



In 1807 Ferussac {Essai method Conchyl, p. 41) fell into 

 the same error as Bosc and de Roissy. But in 1819 he frankly 

 admitted his mistake {Hist. Nat. Moll., Vol. II., p. 90), and 

 realised that the Teneriffe species had never yet been described 

 or figured — for Ledru's ' Testacula haliotoides ' {Voy. lies 

 Teneriffe, La Trinite, etc., Vol. I., 1810, p. 187) is a nomen 

 nudum. Accordingl}^ Ferussac then gave the first description 

 and figures of the species found in Teneriffe {Hist. Nat. Moll., 



