426 MAZATIAN UNIVALVES 



The completion of the peritreme, and absence of the twisted 

 columella distingn^iish this species from Chemnitzia ; but no 

 plait can be discerned either in the yoiing or old specimen 

 \v^hich are both quite perfect. A broken specimen would 

 probably display it. The species is characterized by the sharp 

 ribs, indented at the suture, with the interspaces elegantly 

 decussated with curved lines. The young shell, with 4 normal 

 whirls, measiires long. -062, long. spir. '037, lat. •032, div. 30°. 

 Adidt, with 7 whii-ls „ '153, „ -113, „ "05, „ 18«. 

 JT«5.— Mazatlan ; 2 sp. off Spondylus ; L'pool Col. 



Tablet 1986 contains the adult specimen. 



517. PPCheysallida clausilifoemis, n. s. 



??Chr. t.valde elongatd, effusa, spird " Claudlice" dextrm 

 simulante ; vertice nucleoso helicoideo, anfractihus ii. et dimi- 

 dio, prominente, verticaliter sito, ah avfractihtis normalihus 

 separata ; marginihus spircc valde excurvaiis ; atrfr. normalihus 

 duohus primis valde tumentihus, vix attingeniibus ; dein anfr. v. 

 suhplanatis, suturis expressis, fascia hipartitd, interdum 

 suhnodulosa ; liridis obsoletis transversis, et striis spiralihus 

 circa hasin effusam indistincte 07matd ; totd superficie minutis- 

 sime iransversim rugulosd ; aperturd ohlangd, ad hasin valde 

 effusd ; plied ohliqud, sttlacnfd ; operculo paticispirali, tenuis- 

 simo, rugulis curvatim radiantihus instructo. 



This most aberrant species is placed here from some of its 

 characters ; others are so peculiar to itself as almost to justify 

 its sectional separation. Its form is that of a dextral Clausilia, 

 with the apex of a very acute Chemnitzia, the nearly smooth 

 surface of Eidimella, and the fold, the operculum, and the 

 constricted mouth of Chrysallida. The peculiarities are the 

 separation and tumidity of the first two normal whirls, and the 

 structure of the suture. This, instead of being impressed, has 

 a sUght raised deposit in each whii'l, which meets its neighbour 

 like the rims of two ))lates. .111 the four specimens found were 

 imperfect and disintegrating ; in one of them however the 

 operculum, as weU as the vertex, were preserved. The largest 

 must have measured when perfect, long. *15, long. spir. *095, 

 lat. -aiS, div. 20". 

 Sah. — Mazatlan ; 4 sp. off Chama ; L'pool Col. 



Tablet 1987 contains the least imperfect specimen, with its 

 operculum. 



