102 JOURNAL OF CONCHOLOGY, VOL. II, NO. 4, OCTOBER, I904. 



As Scopoli's "Introduction to Natural History" is a rare book, and 

 as I have only been able to consult it through the kindness of friends 

 who have sent me copies of the portions relating to this matter, it 

 will be convenient if I explain his method of arrangement, for this is 

 an essential part of the question. Scopoli divides the bivalves into 

 two orders, under the headings "Distributio I., cardine edentate," 

 and "Distributio II., cardine dentato." Under the first head he 

 placed the genera Anomin, Ostrea, Mytihis, and others ; under the 

 second head he placed the genera Volsella, Pteria, Solen, and others. 

 It is clear, therefore, that by his own method of arrangement Volsella 

 must be a group of shells which possess a toothed hinge, which 

 Modiola does not. In other words, "cardine dentato" must be read 

 into the definition of every genus included under his Distributio II. 

 The first of these genera is Volsella, which is thus defined : — 



"Testa bivalvis, cardo sulcus longitudinalis, obsoletus, quem 

 terminant denticuli exigui, vix manifesti. 



Mytihis modiolus Linn., dente unico. 



Giila soricis Lister, dentibus 1-2. 



Mytilus, Laber Adanson, dentibus pluribus." 

 Now, those who wish to substitute the name Volsella for Modiola 

 rely on the rule of taking the first species mentioned by the author of 

 a genus as the type of the genus, whether he meant it so or not ; in 

 this case it is Mytihis modiolus, which is the very species afterwards 

 taken by Lamarck as the type of his genus Modiolus (so spelt in 

 1799). If Scopoli had made no mistake there would be no more to 

 be said, for the priority is unquestionable, but he described M. modiolus 

 as having a single tooth (dente unico), and he expressly states that 

 both his other examples have teeth, while in his definition of the 

 genus he says it has small teeth at the end of the hinge. It is, there- 

 fore, abundantly clear that he would not have put any shell into this 

 genus if he had not believed that it possessed hinge-teeth. It is 

 obvious that he intended to leave those species of the Linn^ean genus 

 Mytilus which had no teeth under that name, and to create a new 

 genus for those which had teeth (one or more). 



How Scopoli came to imagine that Af. modiolus had a tooth at 

 either end of the hinge, it is impossible to understand, and probably 

 we shall never know, but as this species does not occur in the 

 Mediterranean, he may only have known it from figures. Anyway, 

 he did make an extraordinary mistake concerning it, and in conse- 

 quence of this mistake it seems to me unreasonable and impossible to 

 follow the usual rule of taking the first species as a type. It is in 

 this case disqualified by the fact that its characters are not those of 

 the genus Volsella, as defined by Scopoli himself. To make it the 

 type of a genus with a toothless shell under the name of Volsella 



