AND DESCRIPTIONS OF NEW SPECIES. 105 



Cabinet of the Lyceum of Natural History of New York. 



Cabinet of the Academy of Natural Sciences of Philadelphia. 



Diam. five-twentieths, Length four-twentieths of an inch. 



Remarks. — This very curious and interesting species was among the 

 fresh water shells so disinterestedly sent to me by the Lyceum of Na- 

 tural History of New York to be examined and inserted in this paper. 

 It has the singular property of strengthening its whirls by the agglu- 

 tination of particles of sand, &c. by which it is entirely covered, and in 

 this character it resembles the Trochus agglutinans,Ijam. (Trochus 

 conchyliophoriis, Authors.) The apex in all the specimens which I 

 have had an opportunity of examining is broken. The operculum was 

 observed in two specimens sufficiently perfect to exhibit a striated 

 horny structure. 



SUPPLEMENT. 



Read before the American Philosophical Society, May 20th, 1831. 



SINCE my Memoir, read before the Society last May, went to press, 

 I have procured several species which I believe to be undescribed : and 

 which I now propose to add as a supplement, with some preliminary 

 observations. 



Having had an opportunity to examine many fine specimens 

 within a few months, particularly those brought to this city by James 

 Ronaldson, Esq. to whose kindness I am indebted for some very rare 

 species, I have had an opportunity of observing some colouring of the 

 nacre which is exceedingly beautiful and rare. It is a singular fact, 

 that several species, which may be considered, emphatically, as white in 

 the nacre, vary slightly by being possessed, very rarely, of a tint of pink 

 in the lateral and sometimes in the cardinal tooth or in the centre of 

 Vol. IV.— 2 B 



