358 MAZATtAN UNITALYE3 



Tablet 170G contains a series of 11 specimens of different 

 ages, beginning from '027 by '018, and presenting tbe extremes 

 of variation, — 1707, 2 sp. alabastrine variety, and as a contrast, 

 one vdth black incrustation ; also 2 fragments to illustrate the 

 adolescent and the adidt basal scidpture. 



Genus EISSOA, Freminville. 



Bull. Soc. Pliilom. 1814, p. 7. 



Loxostoma, Bivon. 1832. — Lamarckia, Leach. — Gonostoma, 

 MiWf. 



411. PRiSSOA LIE ATA, n. s. 



? R. t. conoidea, alhido-fuscd, soUdiore ; anfr. vi., quoinim ii. 

 primi tumidiores, Icevi ; reliqui planati, eleganter Hrati, lins 

 plurimis fin spird circiter x.J extantibus, interstitiis cequantihus, 

 quadratis ; sulco latiore circa peripheriam, suturam swperante ; 

 anfr. radiatim obsolete undatis, prope suturam subnodosis ; 

 marginibus spirce excwrvatis ; basi subangulato ; apertura sub- 

 ovali, peritremati continuo ; labro antice expanso : opereulo 

 solidiore, cornea, rufo-fusco, semilunato, convexo ; elemeniis C07i- 

 centncis ; nucleo subcentrall, marginem interiorem versus ; intus 

 processu conico anteriori prcelongo, extante, costd ad alterum 

 marginem deeurrente. 



Of this beautiful shell one perfect specimen was found with 

 its operculum. This makes its generic position doubtful ; as 

 it presents the concentric elements of Jeffreysia and the 

 anteriorly projecting process of Rissoina, in conjunction with 

 a shell typically Rissoid. The nucleus is projecting, and 

 situated about half way between the centre and the inner 

 margin. It appears that the entire sculptured layer may be 

 abraded ; for a specimen was found (which but for one in an 

 intermediate state woidd surely have been regarded as a dis- 

 tinct species) without either lira; or transverse waves, and 

 scarcely shewing the sutural furrow ; but with a smooth surface 

 most delicately corrugated transversely. Long. '12, long, 

 spir. -073, lat. '063, div. 25". 



Hob. — Mazatlan. ; 9 sp. off Chama and Spondylus ; L'pool Col. 



Tablet 1708 contains the perfect and the abraded specimens. 



