362 MAZATLAN UNIVALVES 
419. JEFFREYSIA* BIFASCIATA, 2. s. 
J. t. subelevata, diaphand, tenuissimd, levi, anfr. v. subtumi- 
dis, sutura impressd ; lined spirali subsuturali ; anfr. primo 
minutissime granulato ; pallide fused, fasciis spiralibus duabus 
JSuscis ornata ; aperturd subovali, peritremati continuo, umbilico 
minimo ; operculo rufescente, haud tenuissimo. 
Variat t. plus minusve elongata ; colore quoque pallido seu corneo. 
Of this species, beautifully lustrous when viewed under the 
microscope witha good light, about 90 specimens were obtained, 
probably from the Algz on the Uvanille. They are most likely 
of somewhat sedentary habits, as even in a living state they 
are not unfrequently incrusted with Coralline. The dried 
animals have a rich brown colour. Several retained their 
opercula, which are perfectly normal, and of a reddish brown. 
Long. 055, long. spir. ‘032, lat. °03, div. 30°. 
Hab.—Mazatlan ; rare, on PAlge ; L’pool Col. 
Tablet 1716 contains 3 sp. richly coloured, of which 2 retain 
their opercula.—1717, 3 sp. pale non-banded variety, one with 
beautiful incrustation of Coralline. 
420. P JEFFREYSIA ALDERI, 2. s. 
J.t. “SJ. bifasciate” simili, sed solidiore, multo majore ; anfr. 
v. magis planatis, fasctis angustis. 
Three dead specimens were found on Chame which appear 
to be a distinct species. Of the very numerous specimens of 
J. bifasciata, none approached it in size, though the number 
of whirls is the same. The station appears to be different, 
and the whirls flatter. It is dedicated to one who stands 
unsurpassed for accuracy and courtesy among British Malaco- 
logists, and to whom we owe the first full description of this 
very interesting genus. Long. °068, long. spir. °035, lat. ‘O44, 
div. 35°. 
Hab.—Mazatlan ; extremely rare, on Chama; L’pool Col. 
Tablet 1718 contains the least incrusted specimen. 
* As a name, Rissoella has precedence; but as the first accurate account of the 
enus was given by Alder, it seems fair to adopt his designation; especially as 
Rissoid names are sufficiently plentiful, and the other is at the same time dis- 
tinctive, and preserves the remembrance of one of the most accurate labourers 
in British Malacology. Philippi has settled the difficulty by adopting both 
names as separate genera, of which he places Jeffreysia in Paludinide and 
Rissoella in Eulimide. 
