MUSEUM OF COMPAKATIVE ZOOLOGY. 89. 



are only provisionally referred to Cerithiopsis, and may hereafter be proved to 

 belong to Bittium or to some allied group. Were the describers of new genera 

 and subgenera to carefully describe the distinctions between the groups they, 

 name and their near allies, much labor would be saved those who come after, 

 and who have to do the drudgery properly belonging to the original describer, 

 if indeed he went so far as to give the data necessary for the search. Many 

 genera really separated from one another by good characters are defined by 

 most worthless ones in the text-books, and in no department is there more 

 work to be done than in what may be termed that of giving a proper perspec- 

 tive to the innumerable named groups of mollusks. 



This particular species is clearly different from any of those described by 

 Watson, and I have been unable to find any described species with which it 

 agrees. 



Cerithiopsis (?) crystallina n. s. 



Shell translucent white, elongate-conical, extremely acute, with granulated 

 surface and about twenty-four somewhat rounded whorls ; nucleus extremely 

 minute and partly submerged, smooth, shining, translucent, passing impercep- 

 tibly into the very attenuated shining apical whorls, which in the adult are 

 most frequently, though not always, lost ; spiral sculpture in the earlier 

 whorls of two rather strong subequal rounded revolving riblets, to which, 

 about the seventh whorl, another smaller thread just before the suture is 

 added, which soon becomes nearly as prominent as the posterior riblet of the 

 original pair ; the space between the original pair gradually grows propor- 

 tionately wider, and about the tenth whorl a fine intercalary thread appears 

 which always remains smaller than the others ; beside this in the nearly adult 

 shell the space between the original anterior riblet and the suture (to which 

 this part of the whorl rapidly descends) is supplied with two very fine elevated 

 threads ; a similar one may also (but does not always) appear intercalated be- 

 tween each pair of the four principal spirals above described ; on the base in 

 the fully adult eight or more subequal simple spirals appear between the pe- 

 riphery and the canal, while the more anterior original spirals diminish in 

 prominence and gradually approximate in size to the basal ones ; in the 

 younger shells the difference is quite strongly marked. The transverse sculp- 

 ture in the apical whorls consists of a few (six or eight) rather strong trans- 

 verse riblets, which appear as stout rounded tubercles on the spirals, and run 

 down the spire almost straight, until the order is broken up by the continual 

 appearance of new intercalary series (seventeen on the thirteenth whorl and 

 about twenty-two on the last whorl) ; on the later whorls these are somewhat 

 concavely flexed, and no regular succession up and doAvn the spire can be made 

 out ; fine lines of growth appear on the anterior whorls, which by the constric- 

 tion of the basal periphery put on a rather rounded outline, so that the num- 

 ber of whorls can be easily counted, though the suture is almost invisible ; on 

 the base the only transverse sculpture is due to the delicate lines of growth ; 

 the last whorl or two may lia\e one or two faint varices ; the base is flattish 



