MUSEUM OF COMPARATIVE ZOOLOGY. 189 



distinguished from the type by the absence of the undulations or transverse 

 riblets; the fine sculpture alone is left. Both have a notably large and translu- 

 cent nucleus, much bigger proportionally than is found in any of the shallow- 

 water forms. Its nearest relative seems to be A. obesa. These shells stand 

 about midway between the subgenus Astyris (like A. rosacea) and the small 

 forms of Anachis, and might equally well be referred to either section. 



Subgenus NITIDELLA Swainson. 



In the subgenus Nitidella we have in this region N. nitidula Sby., N. cribra. 

 ria, Lamarck, N. laevigata Linne, N. parvula Dunker, and JV. dichroa Sowerby, 

 the last two being somewhat uncertain as to their subgeneric affinities. Most 

 of these species have numerous varieties and synonyms. Columbella idalina 

 Duclos, a beautiful Antillean species, and G. moleculina Duclos, which extends 

 to the Florida Keys where it was abundantly collected by Hemphill, have 

 much the aspect of Nitidella, and perhaps should be referred there. To the 

 last mentioned species I refer, as a variety, dicomata, a very pretty little form 

 collected by Hemphill on the reefs at Key West. It differs from G. moleculina 

 in being smaller, more distinctly spirally grooved all over, and in having the 

 brown color (on a translucent ground) concentrated in two revolving brown 

 bands, one above and the other below the periphery, the upper one alone being 

 visible on the older whorls. 



Subgenus ASTYRIS (H. & A. Adams) Dall. 



Astyris (H. & A. Adams, 1853) Dall, Proc. Bost. Soc. Nat. Hist., 1870, p. 242; Am. 

 Journ. Conch., VII., 1871, p. 115. 



Out of a number of superfluous names, the present one was selected by me, 

 nineteen years ago, to be used for sundry colored, small, mostly polished little 

 Columbellids which have been scattered through a variety of sections which 

 form phases of a continuous series and cannot be strictly' diagnosed. Of this 

 group there is a goodly number on both coasts of North America and in the 

 Antilles. The species on the east coast of the United States would repay more 

 study than they have received. 



Astyris lunata Sat. 



Columbella lunata Say, Journ. Phil. Acad. Nat. Sci., V. p. 213, 1826 ; Tryon, Am. 

 Mar. Conchology, p. 38, fig. 61, 1873. 



This very common little shell has several absolute synonyms, among which 

 are C Gouldiana (Agassiz MS.) Stimpson and TVheatleyi DeKay. It has also 

 several marked varieties. G. dissimilis Stimpson, of which the U. S. National 

 Museum possesses typical examples, is a rude purplish brown rather large 

 northern form of lunata. None of the specimens so labelled by Stimpson 



