MAZATLAN UNIVALVES 363 



421. JEFFBEYSIA TUMENS, n. s. 



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

 depressd ; a/nfr. iv. convexis, marginibus spirce exeurvatis ; 

 aperturd subovali ; umbilico magno, carinato ; operculo tenuis- 

 simo, translucido. 



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

 very swelling and somewliat irregular whirls, transparent 

 white texture, and large angulated umbilicus. The operculum, 

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

 fectly transparent, appearing black from the remains of the 

 animal, which seems to have been differently coloured from 

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

 div. 55. 



Hob. Mazatlan ; very rare, off Chama and Spondylus ; 

 L'pool Col. 



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

 operculum 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. '044, div. 130. 

 Hob. Mazatlan ; 2 sp. on Chama ; ISpool Col. 



FAMILY TRUNCATELLID^. 



These shells are ranked with Cyclostomidse by Phil, and 

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

 Pyramidellidse by Forbes ; between Dentalium and Pyrami- 

 della by Gray, 1847 ; between Csecum 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. 



