ZOOLOGY. 



The Distribution of M. margaritifera.— Professor Call pub- 

 lished a note in the last number of the Naturalist which seems 

 to demand notice from me, inasmuch as the note appears where 

 readers may see it who have not seen my articles. There are two 

 of these, published in the Journal of the Cincinnati Society of 

 Nat. History, and subsequently, a synopsis of the first, and the 

 whole of the second, in the Am. Jour. Sei. and Arts, March, 1882. 

 My first article appeared in the Cincinnati [<nirn.il, fanuary, 1881. 

 My second in July, 1881. In reference to the distribution of the 

 species under consideration, I said, in the first article, pp. 2 and 

 3. "but among these shells occurs one remarkable anomaly of 

 distribution in the presence of the Margaritana margaritifera 

 Lam., an European species which occurs in the New England 

 States, and, though wanting across the whole interior of the con- 

 tinent, reappears in the drainage of the Pacific slope." Having 

 thus put upon record the general fact of the great severance of 

 these two areas of occupancy, I used the language quoted by 

 Professor Call, in the generalizations of my second paper. 



I may say that I have specimens of this species in my collection, 

 from several streams in the different " New England States," and 

 from various points in the " drainage of the Pacific slope," and 

 that, having given evidence of the possession of the necessary 

 knowledge on this head in my first article, I may have been rather 

 careless about the use of language in mv second, thinking that I 

 had made my thesis sufficiently plain. 



I simply wish to put upon record the fact, that my ignorance 

 of the distribution of this curious species is not so great as Pro- 

 fessor Call's note would seem to suggest. 



As this matter is open for further remarks, I wish to call the 

 attention of the students of this subject to the distribution of the 

 llargaiiiana monodonta Say, originally described by him as a 

 Unio, but which belongs to the present genus without a doubt. 

 Mr. Lea early mentioned the similarity of this species to the M. 

 margaritifera, Obs. vol. VII, p. 43, and vol. x, p. 58. In the first 

 of these articles he says (after having described the soft parts of 

 the M. margaritifera) : " The Unio monodontns Say properly 

 belongs to this genus. Tne soft parts have the same character, 

 and the hard enveloping parts are very closely allied." In the 

 second of these references he says (following a discussion of the 

 soft parts of Monodontus): "The form of the outer hard parts, as 

 well as the soft parts, is so different from other Unionidae, except 

 Margaritana margaritifera that we might expect to find a strong 

 variation in the important part of the embryonic shell, but, un- 

 fortunately, we have not yet seen the embryonic shell of either of 

 them," etc. Now while there are differences in these two mollusks, 

 sufficiently emphasized to separate them as species, there are 

 numerous characters pointing to their close alliance, and as I have 



