30 THE NAUTILUS. 



spicuous at the margins of the impressed ray; posterior cardinal 

 margin nearly straight, anterior ditto evenly rounded ; interior por- 

 cellanous white, the pallial sinus not reaching the middle vertical 

 line of the shell, broad and rather rounded; ligamental fosset large, 

 cuplike; anterior teeth V-shaped, about 22 in number, strong and 

 prominent; posterior teeth similar, and forming an equally long line 

 but only 18 in number, the posterior cardinar margin showing a 

 long narrow impressed area very feebly marked ; length of shell 

 32; beak from anterior end 12; vertical from beak to base 17; 

 max. diameter 13 mm. 



Habitat U. S. Fish Com. Station, 3202, in 382 fathoms green 

 mud, Monterey Bay, California, bottom temperature, 41° Fahren- 

 heit. 



This fine shell recalls Y. tliracuejormis, but is smaller, without the 

 angularity of that species and proportionately more solid. It was 

 dredged by the U. S. Steamer Albatross, several years ago. It is 

 probably a deep water species exclusively at least in the latitude of 

 California. The types are in the U. S. Nat. Museum, 106,972. 



NOTES ON THE GENEKA OF UNIONID^ AND MUTELID^. 



BY H. A. PILSBRY. 



In the June number, p. 20, a list of the genera of Unionidce and 

 Mutelidce recognized by Dr. v. Ihering is given. It should be noted 

 that by inadvertence Pleiodon Conr. is given as a genus, but Iher- 

 ing considers it a synonym of Irklina. The genus Pseudodon Gld. 

 was omitted after Cristaria Schum.^ 



Attention should also be directed to the fact that the name Cas- 

 talia Lam., 1819, is preoccupied in Vermes by Savigny, 1817 (Sys- 

 teme des Annelides). Probably Tetraplodon Spix, 1827 can be 

 used in this case as a substitute. 



For Aplodon Spix (preoc. by Rafinesque in Pulmonata), may be 

 substituted Spixoconcha, 



Lea's name Plagiodon (1856) seems also to be preoccupied (by 

 Dumeril in Reptilia, 1853), and the group may therefore be called 

 Iheringella, Lea's species isoeardioides being the type. 



^ The Editor fears that these errors may have been due to his own hasty proof- 

 reading, rather than to defects in the original MS. 



