INVERTEBRATE PALEONTOLOGY. 181 



four years later, in which latter volume he associated the animal of Mactra 

 and other types with Callista and Cattistoderma* 



From the species thus cited by Poli at the time he first proposed the 

 name Callista, il is evident that the group, as he understood it, was complex, 

 or, in other words, made to include species belonging to more than one genus ; 

 and, consequently, any subsequent author had the right to separate, under 

 other generic names, the group or groups to which some of his cited species 

 belong. The first author who did this, so far as I have been able to ascer- 

 tain, was Lamarck, who, in 1799, proposed the name San guinolaria for a 

 group that would, according to high authority, include V. dejlorata, Linn. 

 Next, in 1811, Miihlfeldt proposed a genus Chione for another genus that 

 includes V. gallina, Linn. ; thus leaving the species Venus chione, Linn., 

 alone to represent Callista, Poli. So it would seem that, whether we follow 

 the rule of taking the first species mentioned by an author under a new genus 

 as its type, or the rule of elimination, if I may so call the separation of extra- 

 neous types from a complex genus, Venus chione, Linn., would be the type of 

 ( 'allista, Poli ; and as the law of priority requires that a generic name once 

 regularly proposed must be retained by subsequent authors for the group to 

 which some one of the included species belongs — provided that any of them 

 belong to a genus not previously named — it appears to me clearly evident 

 that Callista, Poli, must stand for the genus here under consideration, includ- 

 ing Venus chione, Linn. 



I am aware that, in 1838, Dr. Gray proposed the name Chione for a 

 genus, with V chione ats its type ; but this could not stand, not only because 

 this species, as above shown, is the type of the older genus Callista, but also 

 because the name Chione, was pre-occupied, as already shown, by another 

 genus, named by Megerlc von Muhlfelt, in 1811. Dr. Gray also named 

 another section D/one, in 1847, with V. dione, Linnaeus, as its type ; but as 

 all other authorities agree that this shell is congeneric with the genus here 

 under consideration, the name Dione necessarily falls into the synonymy of 

 Callista, though it may be retained in a subgeneric sense for a subordinate 

 section of that genus. 



As here defined and understood, it can scarcely be affirmed on satisfac- 

 tory known evidence, that the genus Callista dates back farther than the 

 Cretaceous epoch ; though it is possible that some of the similar Jurassic 



• Mr. Conrad had evidently not seen PoW'sfirst announcement <>f Callista, 1791. 



