PYRAMIDELLIIXS!. 411 



The Chem. fenestrata is very distinct, as is the elegant 

 C. scalaris, which latter we have frequently, during the last 

 thirty years, taken at Exmouth, varying in the number of 

 ribs, but never in a living state. Since then, both have been 

 taken alive, and, in the examinations, we have ascertained 

 that the Chem. rufescens of the ( British Mollusca ' is only a 

 variety of the " scalaris." We have shown, in the descriptions 

 of Chem. interstincta and C. indistincta, their specific points, 

 and that the Chem. clathrata is scarcely a variety of the 

 latter. 



The elegant C. decussata, the " arenaria" of Montagu, 

 abounds at the same place in the coralline zone, and with 

 the well-known C. Scillcs and C. acicula require no remark, as 

 they are undisputed species. 



The C. affinis of authors, we believe, is a variety of the 

 C. acicula, a very variable species in respect of the tumidity 

 of the volutions and depth of the divisional lines, as well as of 

 the texture of the shell. The C. clavula is very distinct, and 

 everything relating to former impressions is fully explained 

 under that title. We think the Aclis nitidissima of authors 

 will, when the animal is observed, prove a Chemnitzia ; the 

 Aclis unica, formerly conjectured by me to be a Chemnitzia, 

 has this year (1854) been discovered, and is described as Rissoa 

 unica, in the elongated section of that genus. 



The beautiful Chemnitzia Gulsona is our own discovery 

 more than thirty years ago. I have not a character to add or 

 omit from my original description in the Annals of Natural 

 History, except that after the phrase of the specific character, 

 "peripheria integra," interdum interrupta may be added, as 

 my specimens differ. The apex is subreflexed indeed every 

 character denotes the Chemnitzian animal; there is not a 

 single point of the Rissoa in it. 



The Chem. formosa is a slender Chem. rufa. 

 The beautiful, but common, Chem. elegantissima is the 

 staple commodity amongst the shells at Exmouth, where all 

 its varieties occur, but never alive probably because they 

 inhabit the rocky portion of the laminarian zone, far beyond 

 the lowest tides, where the dredge cannot work ; they must 



