MAZATLAK UNIVALVES 



363 



421. Jeffeeysia tumens, n. s. 



J. t. tumente, diaphana, Icevi, tenuissimd, albidd ; vertice 

 depressd ; anfr. iv. convexis, mm-ginihus spira excurvatisj 

 aperturd suhovali ; umhilico magno, carinato ; operculo tenuis- 

 simo, translucido. 



Differs from tlie least elevated form of J. bifasciata in its 

 very swelling and somevrhat irregular wliirls, transparent 

 white texture, and large angulated umbilicus. The operculum, 

 wbicli was found in five out of the thirteen specimens, is per- 

 fectly transparent, appearing black from the remains of the 

 animal, which seems to liave been differently coloured from 

 that of J. bifasciata. Long. '048, long, sjiir. -026, lat. '038, 

 div. 55". 



JECab. — MazSiilaD. ; very rare, off Chama and Spondylus ; 

 L'pool Col. 



Tablet 1719 contains 2 sp. ; one young and glossy, with the 

 opercidum so situated as to shew the medial process ; the 

 other adult. 



422. ? Jeffeeysia , sp. ind. 



Tablet 1720 contains a horny, transparent shell of three 

 whirls, exactly like a small Ampullaria. It may possibly be a 

 nucleus, but is much more normally shaped than the many 

 such that I have examined from this collection. Another im- 

 perfect specimen was found with an additional half whirl. 

 Long. -046, long. spir. -009, lat. 'OU, div. 130". 

 JIab. — Mazatlan ; 2 sp. on Chama ; L'pool Col. 



Family TRUNCATELLID^. 



These shells are ranked with Cyclostomida) by Phil, and 

 C. B. Ad. ; with Littorinida* by Woodward ; doubtfully with 

 Pyramidellida5 by Forhes ; between Dentalium and P.n'ami- 

 della by G-ray, 1817 ; between Cfeeum and Pyramidella, do. 

 1850 ; between Lacuna and Planaxis, do. 1855. For an account 

 of the animal of the Tr. Montagui, v. Clark Moll. Test. Mar. 

 Br. p. 380, according to whom it is an undoubted Littorinid. 



