OP CONCHOLOGY. 109 



This shell has been considered identical with Chrysodomus 

 decemcostatus, of Say, by Drs. Middendorf and Carpenter. Mr. 

 W. Cooper separated it under the name of Middendorfii, being 

 ignorant of Martyn's publication. 



. Having dredged a very large series of this species on the 

 north-west coast, and having had the opportunity of comparing 

 an also very extensive series of eastern specimens dredged by 

 Dr. Wm. Stimpson, materials upon the authenticity of which no 

 doubt could be thrown, were in hand for examination. 



I availed myself, with much interest, of the opportunity thus 

 afforded for a careful comparison. The results are as follows : 



Proportional length of the aperture, including the canal, to 

 the spire, from the posterior sinus of the mouth to the apex : in 

 twenty-five specimens of liratus 32 x 13 ; in the same number 

 of decemcostatus, 30 x 18. Average number of revolving 

 ribs in liratus, twelve ; in decemcostatus, nine ; maximum in 

 liratus, fifteen ; minimum, nine ; maximum in decemcostatus, 

 eleven ; minimum, six. Width to height in liratus, 17 x 32 ; 

 in decemcostatus, 14 x 22. Maximum length of liratus, six 

 inches ; of decemcostatus, four inches. Maximum width of liratus, 

 2*4 in. ; of decemcostatus, 2*2 in. Average relation of height to 

 width in liratus, 2*2 to 1 ; in decemcostatus, 1*63 to 1. 



The following comparative characters have also been noted : 



0. decemcostatus. C. liratus. 



Animal frequently pure white, Animal always black spot- 



sometimes flecked with black- ted ; end of siphon and probos- 

 ish. cis black. 



Shell with posterior part of Shell with posterior part of 

 whorl generally tabulate or whorl rounded, making a smaller 

 concave. Ribs strong, in adults angle with the suture ; often 

 broad and flattened on top, with more or less strong ribs 

 interspaces usually channelled, above the first prominent rib. 

 lightly grooved or smooth. Ribs slender, more equal, less 

 General shape of shell less elevated, not flattened on top ; 

 fusiform, and whorls less interspaces not channelled, 

 rounded. Aperture white ; strongly grooved, often, with 

 channels corresponding to the with quite prominent interca- 

 ribs, sometimes chestnut brown, lated ribs. Aperture purple 



or livid ; if partly white, the 

 white is in the channels cor- 

 responding to the ribs, with the 

 interspaces purple. 

 Siphonal fasciole broad, exca- Siphonal fasciole long and 



vated, and with the fold strong, slender, usually nearly obso- 

 lete, sometimes quite so. 



