OF CONCHOLOGY. 91 



unreservedly that no constant differences whatever are to be 

 found between the true recent and fossil marine Corbulce and 

 the species of Anisothyris ! 



The teeth, muscular impressions, beaks and sculpture vary 

 among the species of Corbula as they do among the species of 

 Anisothyris and so on interchangeably. 



Taking any one of the characters which at first sight appear 

 to characterize Anisothyris, and comparing its different species 

 and the different species of Corbula, it will be found that 

 there is as much difference between the different species of the 

 former as there is between some of its species and species of 

 Corbula. 



Neither the obliquity of the beaks, nor their spiral form, nor 

 the inequivalve shell, nor the form and size of the teeth, nor 

 the hinge line, nor the external sculpture, nor the general form 

 of the shell, have any generic constancy, or difference (except in 

 gradual and almost insensible degrees) from true Corbula 1 . The 

 muscular impressions, pallia! line, &c, are relatively and pre- 

 cisely similar in both, with the exception of differences which 

 are not constant in the same species. 



I therefore feel hardly justified in retaining the name at all, 

 and only do so because, on the whole, there is a general physi- 

 ognomy which is somewhat peculiar, though valueless when 

 subjected to rigid criticism ; and the following characters are 

 especially emphasized in most of the species. 



The beaks are usually (but not always) more oblique and more 

 posterior and more spiral than in most Corbulas, and the ex- 

 ternal surface is usually smoother, though often exactly like that 

 of typical Corbulas. In consequence of the obliquity of the 

 beaks the teeth and hinge line are similarly affected in such 

 cases. 



I feel entirely warranted in asserting that no positive diagno- 

 sis can be drawn up, including the characters of all the species 

 of Anisothyris, which will not apply as well to the genus Corbula 

 as a whole. 



The type of the group is Anisothyris obliqua, of Gabb, (1. c. 

 p. 199.) 



Mr. Woodward, forgetting the axiom, that " a name is a name 

 and not a definition," changes the A. tenuis, Gabb, to A. Haux- 

 welli, Woodw. This proceeding is akin to those of the earlier 

 authors, who have created in this matter so much confusion for 

 later students, and it is to be hoped that it will be reprobated as 

 it deserves by other authors. The only basis for the change 

 consists in the opinion of Mr. Woodward that the shell is not 

 "thin!" It would be well for him to consult the preface to 



