RISSOA. 371 



An account of the R. cingilla has appeared in the ' British 

 Mollusca/ The R. pulcherrima, nonnull., is a dwarf, nearly 

 ribless R. inconspicua, which is one of the most variable species 

 in form, size and markings. In comparison, care must be 

 taken not to examine what is called an adult R. pulcherrima 

 with a young ' inconspicua ' of the same size, but of larger 

 growth, as it may lead to false ideas of distinctness : adult 

 shells, of whatever growth, and in like manner, young shells, 

 must be compared together, as the aperture in the two condi- 

 tions is very different, there being in that of the young ones 

 always a subangularity, but in those with completed peristomes 

 it is nearly orbicular. 



I have lately received some minute shells collected in Zet- 

 land ; I have met with them occasionally on the South Devon 

 coast. They are a partly dwarf or immature variety of 

 that singularly variable species the Rissoa inconspicua, and 

 are marked in the direction of the axis with about seven 

 brownish-red lines that are tolerably regular and equidistant. 

 I believe they are the long-lost species of Adams, "lineis 

 rubris notata. Apertura margine patentissima." (Linn. 

 Trans, vol. iii. p. 67.) With respect to the thickened or 

 broad margin, it is rarely seen but in the completed shell, 

 whether it be dwarf, or of a larger growth ; and in the variety 

 styled pulcherrima it is mostly wanting, probably in conse- 

 quence of a depauperation from littoral causes, as the R. in- 

 conspicua is usually a deep-water or coralline zone species. 



The so-called R. eximia is an undoiibted Chemnitzia allied 

 to C. excavata ; I have described the shell, the animal being- 

 undiscovered, under the title of C. Barleei. I cannot speak 

 of the R. anatina and R. ventrosa, not having met with them 

 alive. 



The Turbo subumbilicatus of Montagu is still in obscurity ; 

 it is perhaps a variety of one of the species of the estuaries, 

 and if it could be identified, its position would probably be in 

 this genus. I mention the Jeffreysia diaphana and /. opalina, 

 because they have recently been styled Rissoce ; they appear 

 from several characters to form the passage to the Chemnitzice. 

 I think I have now named every Rissoa. 



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