SCROBICULARIA. 433 



than to the group in question. Out of five species 

 which Da Costa assigned to Trigonella, the first four 

 are the only kinds of Mactra that appear to have been 

 known to him ; and as to the last (our S. piper at a), he 

 observes that " the hinge of this kind is of a different 

 structure from the Trigonellce" Montagu's genus Ligula 

 (1808) is the next in order of date; but his diagnosis 

 was principally intended for Thracia ; and the present 

 genus was indicated only in the alternative, and insuffi- 

 ciently, viz. " in some species a minute erect tooth." 

 He enumerated six species, arranged in two equal divi- 

 sions : the first comprised all those of Cochlodesma and 

 Thracia which he had discovered; and the second S. 

 piperata, S. tenuis, and S. alba, to which he subsequently 

 added S. prismatica and Montacuta substriata, although 

 with some doubt as to the generic position of the last- 

 named species. But at all events it would be inconve- 

 nient to have Ligula in the Mollusca, because the name 

 was preoccupied by Bloch in 1782 for a genus of Entozoa, 

 and (having been adopted by Rudolphi and others) is now 

 constantly used in that department of zoology. Arenaria 

 (1811) of Megerle von Miihlfeldt succeeds ; and although 

 it has been lately revived by Gray and Morch, it is a 

 Linnean and familiar botanical genus ; and the current 

 of scientific opinion seems to be against the double em- 

 ployment of any such name in natural history, if it can be 

 avoided. I do not myself see any objection to the same 

 generic name being used in marine zoology as well as in 

 land botany, considering how wide apart are these great 

 hemispheres of Nature, and the remoteness of the pos- 

 sibility that any practical inconvenience would ensue. 

 However, Schumacher gives this as the sole reason for 

 changing Arenaria into Scrobicidaria (1817); and as 

 the alteration has been sanctioned by Philippi, Forbes 



