MAZATLAN UNIVALVES 445 
562. CERITHIOPSIS DECUSSATA, 2. S. 
C. t. conicd, gracili, subcered, albidd, ad basin rubro-fusco 
fasciatd ; (2anfr. primis vi. levibus, prominentibus ;| anfr. 1x. 
normalibus, carinis validis, obtusis, circa spiram 11., ad et infra 
peripheriam ii. acutioribus ; interstitiis subquadratis, @ lirulis 
parvis radiantibus distantibus, ad peripheriam continuis, decus- 
satis ; carinis spiralibus locis decussatis subtuberculosis ; labro 
tenut ; labio vie distincto. 
Only one adult specimen was found of this beautiful species, 
intermediate in sculpture between C. assimilata and C. tuber- 
culata. The transverse lire seem to pass under the stout keels, 
which are then raised into dull tubercles. The description of 
the nucleus is given with doubt, being supplied from a young 
shell, with only one normal whirl, which therefore does not 
affiliate with certainty to the adult. Long. °16, long. spir. *12, 
lat. ‘045, div. 17°. 
Hab.—Mazatlan ; extremely rare, off Chama; L’pool Col. 
Tablet 2034 contains the specimens. The lip of the adult 
was unfortunately broken in extracting a minute pebble. 
563. CERITHIOPSIS AssImMILATA, C. B. Ad. 
Cerithium assimilatum, C. B. Ad. Pan. Shells, pp. 150, 309, 
no. 194. 
 Cerithiopsis assimilatum, H. & A. Ad. Gen. 1. 240. 
Comp. C, terebellum, C. B. Ad. (Jamaica) in Sow. Thes. Conch. 
Comp. C. trilineatum, Phil. in Sow. Thes. Conch. 
Another allied but very distinct species is C. cereum, Sow. 
from Australia. The Pacific shell is known by its dark reddish 
brown colour, nearly straight outline, very narrow sharp ribs, 
with the broad interstices elegantly decussated. The Mazatlan 
shells are shorter in proportion and of a lighter colour than 
Mr. Cuming’s type specimens, in which respects they closely 
resemble C. terebellum. ‘They differ in the sharpness of the 
ribs, which in that species are flattened and broader. There 
are five ribs, of which three appear on the spire, one at the 
periphery, and another (smaller) on the base, which is other- 
wise smooth. The first five whirls are smooth and tumid. 
The smallest specimen measures ‘43 by ‘22 ; the largest 
long. °2, long. spir. °145, lat. ‘06, div. 20°. 
Jan. 1857. Pp 
