426 MAZATLAN UNIVALVES 



The completion of the peritreme, and absence of the twisted 

 colurnella distinguish this species from Chemnitzia; but no 

 plait can be discerned either in the young or old specimen 

 which 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, measures long. '062, long. spir.. "037, lat. *032, div. 30. 

 Adult, with 7 whirls '153, '113, '05, 18 e . 

 Hob. Mazatlan ; 2 sp. off Spondylus ; I? pool Col. 



Tablet 1986 contains the adult specimen. 



517. ??CHEYSALLIDA CLAUSILIFOEMIS, n. s. 



??Ckr. t. valde elongatd, effusd, spird " Clausilice" dextra 

 simulante ; vertice nucleoso kelicoideo, anfractibus ii, et dimi- 

 dio, prominente, verticaliler sito, ab anfractibus normalibus 

 separata ; marginibus spirce valde excurvalis ; anfr. normalibus 

 duobus primis valde tumentibus, vix a.ttingentibus ; dein anfr. v. 

 subplanatis, suturis expressis, fascia bipartitd, interdum 

 subnodulosd ; lirulis obsoletis transversis, et striis spiralibus 

 circa basin ejfusam indistincte ornatd ; totd superficie minutis- 

 sime transversim rugulosd ; aperturd oblongd, ad basin valde 

 effusd ; plied obliqud, subacutd ; operculo paucispirali, tenuis- 

 simo, rugulis curvatim radiantibus 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 Eulimella, 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 slight raised deposit in each whirl, which meets its neighbour 

 like the rims of two plates. All the four specimens found were 

 imperfect and disintegrating ; in one of them however the 

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

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

 lat. '045, div. 20. 

 Hab. Mazatlan ; 4 sp. off Chama ; L'pool Col. 



Tablet 1987 contains the least imperfect specimen, with its 

 operculum. 



