MAZATLAN UNIVALVES 445 



562. CEEITHIOPSIS DECUSSATA, n. s. 



C. t. conicd, gracili, subcered, albidd, ad basin rubro-fusco 

 fasciata ; \Janfr.. primis vi. Icevibus, prominentibus ;] anfr. ix. 

 normalibus, carinis validis, obtusis, circa spiram iii., ad et infra 

 peripheriam iii. acutioribus ; interstitiis subquadratis, a lirulis 

 parvis radiantibus distantibus, ad peripheriam continuis, decus- 

 satis ; carinis spiralibus locis decussatis subtuberculosis ; labro 

 tenui ; labio vix distincto. 



Only one adult specimen was found of this beautiful species, 

 intermediate in sculpture between C. assimilata and C. tuber- 

 culata. The transverse lirae 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. 

 Sab. 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. CEEITHIOPSIS ASSIMILATA, C. B. Ad. 



Cerithium assimilatum, C. B. Ad. Pan. Shells, pp. 150, 309, 



no. 194. 



Cerithiopsis assimilatum, H. fy A. Ad. Gen. i. 240. 

 Comp. C. terebellum, C. B. Ad. (Jamaica) in Sow. Thes. Conch. 

 Comp. C. trilineatum, Phil, in Soiv. 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 



