262 On some undescribed Animals of the British Rissoge. 



apology, as without the present close examination, the doubts of 

 their identity or distinctness would still have remained, and the 

 slight though constant difference of contour in the two would by 

 many be considered accidental. 



It may be useful to the shell collector, to the younger student, 

 and as a memorandum of the remaining desiderata of this genus, 

 to offer a few short remarks on all the British Rissoce not enu- 

 merated above. The Rissoa parva, the type, has been described 

 in the 5th volume of the 'Annals,' N. S. p. 359; I have there 

 mentioned that the R. rufilabris, R. costulata, and R. interrupta 

 are varieties of the type, to which I believe I may add the 

 R. labiosa. The R. inconspicua has been spoken of by Mr. Alder 

 in the ' British Mollusca •' I will therefore only say, that having 

 examined the animals of numerous specimens of its varieties, I 

 find no marked variation ; they all have the lead-coloured stripes 

 on the alse and sides of the foot. I have also stated in the ' An- 

 nals/ N. S. vol. vi. p. 33, that I thought it a coralline zone va- 

 riety of jR, parva ; I withdraw that opinion, as I am satisfied of 

 its distinctness. The animal of the elaborately sculptured R. 

 striatula, the most elegant of the Rissocc, if it be one, still escapes 

 observation. I have this summer taken some delicate specimens 

 in the coralline district, and yet hope to see the inhabitant. 



The R. lactea of Michaud 1 do not know, but from the figure 

 in 'Brit. Moll.' I should have judged it a variety of the R. reti- 

 culata, one of the large, short, tumid shells, and would have 

 said the same of the R. abyssicola, if it had not been considered 

 distinct by Professor Forbes. The R. crenulata is the well- 

 known Turbo cimex, as the R. calathus is the old ' calathiscus ' of 

 authors: neither of the animals are recorded. The R. Zetlandica 

 is a well-established northern species, but the inhabitant is un- 

 known. The R. rubra is very common alive in certain localities ; 

 I have never seen the animal, and can scarcely believe it to be a 

 true Rissoa, as the semitestaceous operculum and its apophysis 

 are more like those of a Chemnitzia. 



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

 Mollusca.' The R. pulcherrima, nonnulL, is a dwarf, nearly rib- 

 less 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 conditions is very different, 

 there being in the young ones always a subangularity, but in 

 those with completed peristomes it is nearly orbicular. The 



