MUSEUM OF COMPARATIVE ZOOLOGY. 283 



in all the specimens. Max. Ion. of shell, 5.3; of last whorl, 3.2; max. lat. of 

 shell, 3.25 mm. 



Habitat. Gulf of Mexico, in 940 fms., mud, bottom temperature 39°.6 F., 

 at U. S. Fish Commission Station 23S4, between the delta of the Mississippi 

 and Cedar Keys, Florida. 



This shell, though shorter and wider, evidently belongs with the last. It is 

 named in honor of Dr. Paul Fischer, whose admirable Manual is so useful, and 

 in fact indispensable, to all students of mollusks. 



Benthonella nisonis n. 8. 



Shell waxen white, with a (slightly damaged) brown nucleus of (more than 

 two) dark polished whorls and eight adult whorls succeeding the larval ones. 

 The shell is almost exactly the shape of a Niso, and if the nucleus were gone 

 would seem to need only the keels to make it one. The whorls are less rounded 

 than in the preceding species, the suture is distinct and slightly appressed. 

 There is no sculpture except that occasionally an emphatic incremental incised 

 line indicates a previous resting stage. Base full and rounded; umbilicus 

 small; aperture beautifully rounded in front, peristome thin, discontinuous, 

 slightly reflected, especially at the inner lip, which is arcuated. Max. Ion. of 

 shell, 9.0; of last whorl, 4.6; max. lat., 4.0 mm. 



Habitat. With the last, in 940 fms. muddy bottom. 



This shell remarkably resembles a Niso without keels, and I should not 

 hesitate so to refer it were it not for the nucleus. The figure of Aclis lata 

 (Plate XVIII. Fig. 8), if the differences of dimension be taken into account, 

 would pretty fairly represent this shell. 



Family CALYPTR^EIDiE. 



Genus MITRULARIA Schumacher. 



Mitrularia Schumacher, Essai, pp. 56, 183, 1817. 

 Calyptrcea Lamarck, 1801 ; not of Lamarck, 1799. 



Mitrularia equestris Linne. 

 Mitrularia Neptuni Schumacher, loc. cit. 



Habitat. Station 2, in 805 fms, Gulf of Mexico; Station 32, in 95 fms.; 

 Station 155, near Montserrat, in 88 fms.; and Station 273, near Barbados, 103 

 fms. Northward to Cape Hatteras, in 15-34 fms., U. S. Fish Commission. 



This group seems to me decidedly nearer Crucibulum, etc., than to Avial- 

 thea, notwithstanding it occasionally secretes a shelly pedestal. 



