THE NAUTILUS. 9 



on the posterior (anterior) side, and in this position has something of 

 a pyramidal appearance. 



For comparison with the author's figures I have figured (PI. I, 

 fig. 3) a topotype from the Fox River, Illinois, the proportionate di- 

 mensions of which are almost precisely those given by Barnes. The 

 comparative measurements, translating Barnes's figures into milli- 

 meters, are as follows : 



Barnes's type : Length 55, height 52.5, diam. 37.5 mm. 



My shell : Length 53, height 51, diam. 34 mm. 



To be of exactly the same proportions as Barnes's shell, the one I 

 have figured should have the following dimensions : 



Length, 53, height 50.7, diam. 36.14. 



That is, the shell figured, as compared with the dimensions of the 

 type, is proportionately .3 mm. greater in height and 2.14 mm. less 

 in diameter than it should be to conform exactly with the type. But 

 the difference is really too small to amount to anything. 



In all other respects, the specimen corresponds with Barnes' de- 

 scription and, making due allowance for the crude drawing, agrees 

 substantially with his figure. I think that there can be no doubt but 

 that the shell I have figured is a typical example of the undatus of 

 Barnes. 



II. 



Is U. undatus Bar.= 7. obliquus Lam. ? 



If the foregoing identification of Barnes's species is correct, it is 

 clear that undatus is not the same as the species, which is to-day 

 universally accepted as the obliquus of Lamarck. For comparison 

 with undatus I have figured (PI. II, fig. 3) a specimen of the species 

 now known as obliquus, of substantially the same dimensions as 

 Lamarck's type. 



A comparison of this figure with those of Barnes needs no de- 

 monstration to show that the two forms are not the same species. 



What species Lamarck really had before him when he described 

 his obliquus is by no means free from doubt. 



His original description is as follows : 



" U. testa sublongitudinali, ovato-rotundata, obliqua, sub-epiderme 

 Candida ; ligamento subduplici; dente cardinali crasso, sulcato, bipar- 

 tite. * * * Habite la riviere de V Ohio. A. Michaud. Distincte de la 

 precedente (liyamentina} par sa forme : elle est renflee vers les crochets, 



